I am a current student at Dartmouth, and it's the same here as well. Especially in a class with a curve, a student is at a serious disadvantage if he/she doesn't collaborate, copy, or cheat.
Setting a strict curve is probably the laziest way to grade a class. It doesn't tell you anything about how well you did (do you get the material? Can you solve problems on your own? Or are you the 27th "best" person in the class?) Of course, with a curve, a professor doesn't have to actually think over what a passing grade is. Which causes all kinds of negative incentive (such as cheating, or almost worse, anti-collaboration). I'll take a class where 10% of the class get an A because the standards are exceptionally high over a class where a strict 40% will get an A, as one implies I'll get a lot out of it, and the other implies I'll stress needlessly over unimportant trivia.
