It can be if you want it to. At Harvard, there's very few requirements on what courses constitute a degree, so if you want to get a degree by just taking the easiest classes possible, you can definitely do that. Of course, most students don't do that since that's not why they went there. I do think professors try to give higher grade averages for the harder classes to avoid punishing students for challenging themselves, but I don't really have a problem with that (if you chose those classes you're probably not in it for the grades anyway). Also, at least I'm the sciences, a good fraction of students start taking classes at the graduate level either freshman or sophomore year, since they'll have completed a good chunk of the undergrad curriculum in high school.