It should be noted though that the iPhone 3GS, iPad 1, and iPhone 4 have the same GPU on their SoC. I think the only difference is the frequency at which it's clocked at.
But I really do agree that it's surprising the iPad 1 isn't on there.
You're right. Just checked. 150 MHz in the 3GS to 200 MHz in the iPhone 4 and iPad.
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I think Apple did do that once, they had support for a device, then dropped support after a few beta releases.
iPhone 3G. They had support into the release of iOS 4 but dropped it at 4.1 or 4.2 because it was awful.