If you do not curve it, you might have 50% of the students getting Fs at lesser schools, which most would not find acceptable. I went to a mid-level college and in a senior/masters level core class I had one prof (the best and brightest) who did not really curve the class. On the mid-term there was a B, seven B- grades, some Cs, some Ds, a non-trivial number of Fs and a non-trivial number of 'not good enough to be an F' grades [40 total]. One A in the class at the end, and one of those B or B- grades got either a D or F for the class. Taught from a book used at Stanford and when I got to grad school I was glad for his rigor, and it was not that hard compared to my harder grad classes at a good, not top, grad school.