I had an iPad 3 since March 2012, just upgraded to the retina iPad Mini in December. Much Better size and I'm sure it will do me well until iPad mini 4th gen!
Had an iPad 2 (64G AT&T) for a little over two years, got a new Air (32GB Wifi) in November...loved both and I think they were/are the two best iPads. Gave the iPad 2 to my significant other and she just loves it.
I have the original iPad and have decided to wait until Apple at least doubles the RAM. The iPad Air and 2nd Gen mini run fine with the 1gb of RAM now but I don't think its enough to run future versions of iOS well enough compared to how long the iPad 2 has lasted. Hopefully I am wrong for everyone has got one and it won't really matter to those who upgrade every year. However for those like me that like to hold onto their tablets for longer than 3 years I'd like it to have more memory for better future proofing.
I get the impression though that Apple is wanting consumers to upgrade their iPads much more often compared to buying a Macbook. By limiting the memory you limit the device's ability to have more processes running in the background which I imagine Apple wants to do with iOS with every new release. I just don't think these things are meant to last that long. Now if I had more disposable income I'd gladly by every new release of every iPad but I still feel the same way in terms of how Apple limits the hardware for future proofing them.