That's unusual. 360 is usually better for that stuff.
http://www.eurogamer.net/articles/di...dogma-face-off
Eurogamer says it's PS3 that suffers the frame-rate drops, although it's a trade-off with screen-tearing in the 360 version. Also, the PS3 frame-rate is a lot less constant.
Basically, you're wrong, and I'll probably get the 360 version :3