@gerbick
WP7 uses XNA framework for their 2d/3dgames. Makes development much easier to be honest. As devs will say it minimises boilerplate code.
Anyway I get what you mean now, but it seems you agree with me for the most part. That software optimisation is the key.

Meego/harmattan optimised for TI OMAP
Android...well I've got no idea, that could explain why some lag, some lag less. Although i expected your Xoom to run games better as it's more powerful. I have played with a Xoom before and i get lags in other places though
iOS optimised for their A whatever. Typical Apple, no surprise
WP7 Mango brings more optimisation to qualcomm