Why is chess dominated by relatively young players?

Well, all you mentioned are probably the reasons for some players.

I would also add 'lack of time' as one of the reasons. When you get older you may need to go to a college/university (chess don't bring much money, unless you are at the top), then family life/kids (chess players have to travel regularly a lot) makes travel harder... So, many people 'switch' to teaching and playing only in local tournaments.


Positional chess understanding in the early game

The main point of the engine recommending exd5 is because it opens up the diagonal from c8 to h3. By playing an early e6, the bad light squared bishop is really weak and has terrible scope, which is why taking with the e pawn could be followed with developing your bishop onto a square on a more open, free diagonal in the future. As long as you castle and don't open up any kingside files, you should be good. As long as your king is safe, an open e file won't do much damage, as his e-pawn is stuck on e-3 (notice white's dark squared bishop; it's basically stuck).
fyi: The whole point of the Slav Defense is to decline the Queen's Gambit with a pawn without playing e6 to block your light squared bishop.


Isolated double pawns like in your example are considered to be both a static and a dynamic weakness. It is a static weakness since the pawns can no longer defend each other or be defended by other pawns. It is a dynamic weakness since the front pawn is blocking the advance of the pawn behind. It is strategically important for the opposing player to control the square directly in front of the pawns, c5 in your example, thereby cramping the movement of both pawns.

However, doubled pawns are often compensated by other dynamical factors, like open files for the rooks and long diagonals for the bishops.

In the Budapest line you are asking about, the move 6.Nbd2 is more popular (than 6.Nc3), leading to a good position for white by simple means.


Strategically speaking, white stands well for several reasons.

Black pawn structure is bad( 2 double pawns(isolated), d6 is
backward)
Black has bad bishop(his bishop  and pawns stands light squares mostly)
Black has less control on dark squares.

For that reason white should do these following steps;

Change the most active Black piece (Queen)
Put the knight a dark square to control light squares(most probably
f4 or c5)
Put his king a center square,
Pressure on c or b file.
White also can exchange 1 or 2 rooks, because black has many
weaknesses staticly.
If white will manage to pass endgame stage, he has strong initiave.


Have you tried one of the more recent forks of Scid?  Specifically ScidvsPC, which is actively maintained.  At the very least it reduces many of the bugs and there are some improvements.  The export to HTML function now includes a javascript option to produce a board viewer for websites, that might do some of what you want.  It will also display annotated games (though it usually won't display any introductory annotations before the first move).  There's also ChessX which looks relatively decent, but I'm not sure how much it will meet your needs.  They're both free, though, so worth a shot.  CheesX runs on Windows, OS X and Linux.  ScidvsPC includes a Mac version, but I can't remember if Linux support is native or needs Wine.

Both of those programs support exporting the PGN to HTML, which is good enough for web pages, but conversion to alternative mark up (or down) languages doesn't seem to have enough demand to have encouraged any development in that field yet.  You might need to code it yourself or conspire with one of the projects under active development to do so.


Karpov's Queen's Gambit beats Kasparov. What is Karpov thinking?

The position after move 9 is the main tabya of the Tarrasch defense. Your feeling that Black is better, or even that he has egalized, is imprecise : White has no weakness, active pieces, and Black's isolani is a long term target. The position is playable for both sides, its evaluation somewhere in between = and +=.

Actually, Kasparov himself stopped playing the Tarrasch after this world championship match ! But of course, this says more about his taste and style than about the quality of the opening itself: others, like Illescas, have made great use of this variation since.

If you want to dig further into the theory of this opening, there are lots of books and DVD on the theme. But I think you will do better to first get familiar with typical 1.d4 games. This Karpov-Kasparov game is an excellent one, and you can easily find it with comments by each of the players (in My Sister Caissa by Karpov or in Dua Matcha and My Great Predecessors : Karpov by Kasparov, also in Kasparov by Nikitin). Analysing commented games is the best way to develop your understanding of an opening and to get a feeling for your new repertoire.


Is there a concept of 'good' knight and 'bad' knight?

I'll answer this in three parts: the literal question, the concept of badly-placed pieces, and the particular example you give.

Bishops are the only piece for which the nomenclature "good" and "bad" is idiomatic. That is because the set of squares a bishop can theoretically travel to is inherent to it; a dark-squared bishop can never ever go to a light square, so if the position is such that you'd like to have a bishop on light squares, you're out of luck and your bishop is "bad". On the other hand, if you have a badly-placed knight (or queen, or rook), there's almost never something preventing you from theoretically eventually repositioning it on a good square. So people generally don't use the term "bad knights".
(People sometimes speak of endgames with a "good knight versus a bad bishop", but this is more a figure of speech meant to call attention to the fact that the bishop is bad and the knight cannot be.)
Pieces can of course be badly placed, but except in the case of a bishop of the wrong color, they are just referred to as badly-placed pieces. In fact an excellent strategical rule of thumb is to always consider improving the position of your worst-placed piece.
However, in the position you present, the knight is doing just fine on f3. It supports an eventual d4 (probably with the support of a pawn on c3), which if played at the right time could be very powerful, opening up the center. It puts pressure on Black's pawn on e5, dissuading him from playing the analogous move ...d5. And in some circumstances it could jump to g5, putting pressure on f7 or h7 (especially after Black has castled).


Stretching the tournament rules, re: capturing pieces

Your opponent has the right to view the board also when it is your turn. If you did this and your opponent complained to the arbiter after a minute or two you would face sanctions. Probably just a warning for a first offence, then a time penalty and if you continue repeating the tactic eventually you would forfeit the game. This loss would be graded as such.