Apple wants to own the tablet market. This is forcing them to get a bit crazy...I think all of the Android competition...and new tablet or phone ever other week...it forced them to update the 2012 iPad ahead of schedule. I had predicted this, but I had I was wrong, but this must been they are feeling a bit shakely in the space.
The iPad 4 is clearly the best tablet in terms of specs right now...so they probably will maintain that lead throughtout 2012. Even google is set to announce a new HD tablet next week, with a higher resolution screen. So Apple has to react. And, since they clearly have the best eco system and app system, they can justify the increase cost of the base models compared to Amazon and Google and Samsung, Lenovo, HP, etc.
If you own a 3, I don't see much of a need to get the 4 so soon. The question should be if you want a mini, in addition to your 3. If you have a 2 or a 1, then the 4 is a good jump. Right in time for Xmas.