The iPad 3, while great, was missing 3 things that would have made it a truly epic update:
1) A6 quad-core CPU
2) PowerVR 6-Series GPU
3) Facetime HD front camera
Don't get me wrong, the 3rd gen is a tremendous update on its own with the Retina display, rear camera, quad-core GPU and LTE, but many of us were expecting the 3 things above. I think the iPad 4 will address all that, and it will be time to upgrade once again in 2013.
And will we hear complaints when the quad-core CPU in the iPad 4 creates more case warmth? Or shortens battery life? Or if the iPad gains another ounce of battery weight to compensate?
If a quad-core CPU with higher performance and better battery life doesn't yet exist, how should Apple add it to the iPad 3? Will there be one for the iPad 4? Maybe, probably. But it's not like Apple's going to wait another year so all the upgrades can be done at once.
Products evolve. While the iPad was revolutionary, each iteration cannot be expected to be just as revolutionary. It must evolve. Just like each new PC from Dell or HP is mostly the same but with a little faster this and a little faster that...
Besides, the display in the new iPad is a huge, huge upgrade. You must realize that you've got a mobile, battery powered device running the same screen resolution as a 27" iMac running off AC power. Yet with no loss of performance from the previous model. That in an of itself is a pretty impressive upgrade.
If it's not enough of an upgrade for you, don't buy it. No one says you must buy a new one each year. In fact, I've suggested to many people that if they're happy with their iPad 2, don't bother unless they really want the new screen or the LTE capability.
I'm not being an Apple-apologist or fanboi, but clearly the iPad 3's specs taken as a whole are better than anything else on the market.
No HD front-facing camera? If that's a deal-breaker for you, then I guess there's not much to be said.