Right, it's not just about the sensor. I don't know specs, but it's safe to say that the 7D likely has a bigger memory buffer to store images. The shutter assembly is likely different, and that's important also. The other part is that the 7D has dual processors whereas the other cameras with the same sensor only have 1 processor.
It's much like 2 cars have the same body, the internals could be entirely different and so one may give you much better performance than the other.