Is there a tag for each build number of Windows on Super User? No. That's because there are too many versions.
Is there enough difference between IDEs to support an IDE version tag? Would it be useful or would it just get in the way?
There's a reason they call them "minor releases." They're... well minor. Most of the differences between versions deal with simple bug fixes, compatibility with new boards, and a few other libraries. IIRC the serial library was updated with Arduino 1.0, but I'm not sure. However, that was a major release (i.e. the first number was changed to signify a big change), so it had a few large changes. I'd imagine that nobody uses something below 1.0, it's kinda like asking should we put a Windows ME tag on Super User?
I've only been playing with the Arduino for a relatively short time, and until recently, it's been very sporadic. I asked a question recently which got the response to try out the latest Arduino 1.5.x as I'm (still?) only using 1.0.5.
Overall, it's not really necessary. Comments work fine... even if the OP says that they have the newest version a common response might be:
Double check that you have the latest version (maybe try the new x.xxx beta version?) and try reinstalling the IDE and any libraries you imported.
I don't feel it's necessary, if it's that important it can be in the body of the post or in the comments. One thing people forget a lot is the purpose of tags: to make finding related items easy. If we split them up, people will have to subscribe to fifteen different tags instead of one. I like the idea of having fairly specific tags, yet not too specific so it's that perfect balance that makes finding data easier.