The only people that will be pissed are the ones that had an iPad 3 and then upgraded to the iPad 4 thinking that Apple will now have a yearly fall release cycle.
All the non-tech perople who bought/got them as presents or their first iPad or an upgrade from an iPad 1/2 will probably not see the point in upgrading and continue to use their devices.
This is true. Thanks to Apple, I've learned to wise up and buy when I need to, not just upgrading for the sake of upgrading. The great thing about Apple products is that they will perform great, years down the line, despite the many revisions following it. I'm still using my 2009 MBP, iPhone 4, and my first iPad which happened to be the 3. The iPhone 4 will be replaced only if it dies or is no longer supported. Other than that, I see no value in replacing it. The iPad will eventually get replaced by an iPad mini as soon as it comes out in retina. Only reason I'm doing it is because the smaller form factor makes sense for me. In fact, I am typing this in one of my children's iPad mini and really digging the size and weight. But yeah, it would be financially irresponsible from my perspective to just upgrade for the sake of upgrading.