Q: which android tablet i should buy for my development which android tablet i should buy for my development?
Do the android OS version matter when doing development for android tablet.
I want that my app covers most used android versions. I took a look at Samsung Galaxy Tab 10.1, it has android 3.1 version. So can i upgrade it to android 4.0 (Ice Cream Sandwich)

A: Well, if you can find one with Ice Cream Sandwich, that's going to cover the most bases in terms of current versions of Android. You may want to take a look at XDA Developers or Cyanogenmod Forums to see if the tablet you are considering is well covered by the modding community as well. I suggest this because if the manufacturer of your new tablet decides it doesn't want to upgrade to Jelly Bean, or whatever, in the future, the modding community may be your best best. 
So those are my two points - try to find an ICS based device, so you don't need to upgrade right away - and so that you can test your app on live hardware for the newest SDK version; and try to make sure the device you are buying is pretty well covered by the modding community. 
I can caution you to avoid Toshiba's tablets, as they have abysmal customer support and do not talk about their planned updates for their devices for months on end. I've not heard great things about the ICS update for Asus Transformers either, even though their Honeycomb is incredible. To be honest, I love ICS alpha 2 on my HP Touchpad. 

A: I would get the Samsung Galaxy 10" tablet. This is the most common size of tablets so you can expect your applications to look good on most tablets.  If you go with an 8.9 inch or 7 inch tablet your applications may not scale perfectly to the 10 inch tablets.  You can always create more layouts to fit each dimension, but I usually try and target the 10 inch tablets first since they are most popular.

A: 
"I want that my app covers most used android versions"

Android 2.3 has the biggest portion of devices in the wild. You can see a break down of the version distribution here: 
http://developer.android.com/resources/dashboard/platform-versions.html
If you're going to target newer releases (and use things like fragments or loaders), you might want to consider using the Compatibility Library to ensure you cover 2.3 and older.
I'd probably +1 for Galaxy 10" tablet - They seem pretty popular, and good modding scene support. I have Xoom upgraded with ICS, and it works pretty well for development. Better then the emulator, that's for sure ;)
