Two weeks could be a bit much, but it really depends on your class size, the format of the exam, and whether or not the professor has TA's helping him grade (as previously mentioned).
Remember, professors have lives, too, and those lives generally include publishing X number of articles/books per year at the school's request (on top of doing the actual research for said articles and book chapters), supervising doctoral students, taking part in whatever board they're on, etc. While it is a professor's obligation to grade exams and get them back to you in a timely fashion, try not to hold them to unrealistic expectations...especially if you have a large class and the test was essay-based.