Thanks for the explanation gerbick I kinda still don't get it though, the 'NEED' that is. Let me ask another question though

Can't a dev just make the aforementioned games for any platform and it will work well? eg. Windows phone currently has Fruit ninja, and I don't notice any dropped frames for example, and they're all qualcomm
Isn't it a matter of the software optimisation that makes these things work sweetly? at this level i.e the era of 1GHZ minimum standard.
Is it possible that your experience with Tegra was because the particular OS it was being used on was simply optimised for Tegras?