At many of the airports I've flown in (as a helicopter pilot), they will also have rotorcraft fly in the opposite direction from fixed wing. Our descent profile and cruising speeds are different than aircraft, and given that we may do confusing things like slow down into a hover, its for the best. Generally they'll place us at a different altitude as well.
As other people mentioned, the fact that larger planes travel at different speeds is one reason they may place them in a different pattern, and I suspect it helps with wake turbulence as well. The planes can be spaced a bit closer together if large planes aren't comingled with the smaller aircraft.
Similar setups will also happen in commonly used airways. For example, where I live in Chicago, and when flying westward through Midway/O-Hare airspace (they overlap), they'll generally have us fly along the highway. They tend to put the rotorcraft at a much lower altitude than the fixed wing, which I suspect is not only for the same reasons as above, but also because the altitude minimums for rotorcraft are lower than for fixed wing, and it gets more traffic out of the way.