I agree. As much as I am a supporter of "good sportsmanship", I think we in the cheer community have a different idea of what is friendly rivalry vs. good sportsmanship. My daughter cheered for her middle school football team this year, and the "smack talk" I heard from the kids and parents -- while EXTREMELY mild -- probably would have shocked many cheer people.
I have thought about this quite a bit since then, and I agree with
kristenthegreat, that the lack of "direct confrontation" on the mat contributes. I also think the fact that the athletes AND spectators mingle in the same arena before, during and after can contribute as well. For many sports, the "smack talk" that is done in the stands is rarely heard by the other team, except for bits and pieces that float over to the other side.
Of course, being able to see and meet people from other gyms is also what makes our sport unique and such a great "community", so we need to take the good with the not-so-good, I guess! I wouldn't trade having met and become friends with people from other gyms!