As I recall, most games were going to have support -- it was going to be games that used undefined or infrequent functions of the hardware that would cause problems.
Regarding games you'd like to see on the list, I suggest giving them time. As this is an area of the console that competes directly with Sony console functionality, MS has an additional incentive to shoot for 100% backwards-compatibility. Can you imagine what'll be said if they achieve this? Things like "The 360 has 100% backwards-compatibility. The PS2 can't even play all PS2 games, much less all PS1 games..."