Is there a difference between rockband for ps2 and ps3?

May be...

also can you earn cash for each gig and use it to buy band gear in ps2?

Well, the only difference I can think of off the top of my head is that you can't buy songs off the Music Store. (I may be wrong though.)



Plus, the fact that PS2 graphics and PS3 are definitely different.



Second question: Yes, you can earn cash for each gig for clothes and gear.