Hmmm, in my orgo I and II classes we used the traditional 90 and above = A, 80 - 89 = B, etc. It was a tough class but the professor's exams were always fair in that if you studied the major concepts discussed during lecture and in the Wade text, there were never any surprises...
Still, I think the grading scale should reflect the difficulty of the course, so it makes sense you might have a modified scale if your class is more difficult. As long as the grade distribution isn't anything too suspect, it doesn't really matter.
I recall that my biochem II class, however, was an entirely different story from Organic II. 70 students, mostly pre-med, all vying for one of those elusive 5 A's the professor gave out during the semester... Only truly cut-throat class I've encountered (fortunately) in which the mean was around a 65%! *still a little bitter about that whole experience*... 🙂