I have not use Physics on any of them. I have seen a few projects that use Physics with nice performance.
So, I tried your "run robot run" game a few moments ago. It's an ok game, I played it 5 times already XD
Still, I have a dual core 1.2 ghz + 750 mb ram android 4.something smartphone and it stutters a bit, even if it's normally playable, but maybe some of the animations just aren't fluid per se.
(Oh, and maybe it's just me, but the red color of the menu buttons kind of gives me the feeling of a "not available" or "pay to have" feature)