Isn't the term a bit condescending?
It could be construed that way, but it depends on what is said after it. If I said:
you wouldn't find it condescending, because generally it is needless to say that two plus two is four.
If I said:
You might, depending on your knowledge of spiders, disagree with the first clause and thus find it a little condescending.
It is up to you to judge your potential audience and tailor your writing to them.
No, it just indicates that the writer expects the fact that follows to not be surprising to the reader. The Cambridge Dictionary Online describes the phrase as:
1) The life and adventures of Martín Chuzzlerwit (Charles Dickens, 1844)
2) The Complete Tales of Uncle Remus (Joel Chandler Harris, Richard Chase, 2002)
I find it is quite the opposite. If you were to neglect to qualify an obvious statement with something like "needless to say", or "as you know", the reader might then feel like he is being condescended to because you are telling him/her information he/she already knows. By adding the qualifier, you establish some common ground, in essence saying "I know that you know what I'm telling you already, and I don't want to insult your intelligence, so please don't be offended."
It is not condescending at all.
It is just a different set of words used to convey the same meaning as '...and hence it follows that ....'
If it were condescending, then the phrase '...last but not the least ...' would also be condescending to the person who is addressed last in some list. Does putting that word 'least' in there mean that there is someone in the room who thinks that person is the 'least' ?
Of course not !
It is just an expression used instead of saying '...it is thus obvious that...', '... it can thus be deduced that...' , '...it implies that...'
Needless to say, needless to say is not condescending at all.