If the iPad is to be a post-PC device, then it should have a support-life that is at least comparable to a notebook computer. It shouldn't have the short two-year support-life of cheap mobile phones.
I expect my iMac to be able to run the most up-to-date version of OS X for at least five years. I've upgraded (high-end) Windows XP machines to Windows 7 without any problems, giving them a shelf-life well over five years. And the iPhones have enjoyed 3 years of OS updates.
Owners get more attached to their PCs than they do to their cell phones, and keep them around for much longer. Taking the iPad 1 off of the upgrade list makes the device feel more like a disposable mobile device than a post-PC device.
I realize that Apple wants to turn over their hardware faster in order to make more money, that the iPad is underpowered, that iCloud backups make hardware transitions a whole lot less painful than they were in the past, and that early adopters of 1st-generation apple productions have historically been screwed (see the original iPhone).
But the iPad is special: it had an unprecedented sales run for a 1st generation device, it has a huge user base, and users have gotten a lot more attached to their iPads than they get to most tech devices.
Rather than worrying about increasing the hardware turnover rate for the next year, Apple should be looking ten years out and doing what they can to not harm the attachment that users have to the iPad brand.
So give us a version of iOS 6. Even a really stripped-down version that wets our appetite for iPad 3s. Make iPads at least as technologically durable as iPhones (2 years of support, 3 years of updates). Give the iPad the added value of longevity.
As Apple has proven to the PC industry time and time again, customer loyalty trumps short-term increases in sales quotas every time. Hopefully they'll remember that lesson in the post-Steve apple.