OK… I think you are blowing things out of proportions. There are very few apps that won’t run on the all WP phones, and I don’t see that as changing any time soon. Are there some, yes, but if you really wanted to play those more cpu/gpu intensive games, you should get a phone that can play them.
I beg to differ though about the Android side of things as far as similarly specified devices. If the 720 ran Android, it would lag, have many app crashes, and not be able to run all of those “advanced” games you seem to want to play. My friend has a HTC desire and complains all of the time about issues.
Just out of curiosity, what games would you like to play, but have the memory limitations you have pointed out?