Also, Gruber later clarified that his guess was not the "iPad 3" per se, but an additional iPad model of some kind, such as possibly a retina display.
I get Gruber's line of reason here, but in the long term it doesn't make sense to me. If we get an additional iPad this September with a Retina Display, what happens to the 2012 iPad? Will it simply receive a bump in resolution, but lack Retina?
All (newer) iOS devices other than the iPad have some form of Retina Display. All iOS devices have an A4 chip (which will become A5 this year). iOS 4.2 unified the iPad, iPhone, iPod Touch lines. Clearly Retina is the one missing feature that's coming to iPad. All iPads.
To me, it makes more sense that Apple would wait until they can build these in bulk, and sell them at the same price point, than to introduce a new top tier $800-$900 iPad (assuming that's what it is) with a Retina Display. Will it have 3 tiers of memory as well and two flavors of 3G? With those options we'll easily see it surpassing the price of a Macbook or Macbook Air. Not quite sure a device that expensive will spur Holiday sales. If we lived in that reality, people would be receiving Macbook Airs like they were stocking stuffers. But Apple's Q1 numbers show us devices that expensive don't move in the numbers that iPods, (subsidised) iPhones, and iPads do.
The only way this makes sense is if this "additional" September 2011 iPad, has other super features that warrant it's "special" release. An iPad Pro for example, with more memory, even more power, and Thunderbolt.
Or if Apple decides to move the iPad introductions to Q1 and do away iPod special events. If iPods are intro'd at this new event, it would be in passing.
New yearly lineup :
iOS event - late March / mid April
iPhone event - June
iPad event - September
iPod / AppleTV (quiet release) - September