I did not take any poli sci classes as an undergraduate either, but took plenty in route to my masters in IR. I don't know about you, but I worked my butt off in grad school to get the grades that I got, harder than I ever did as an undergrad, so I don't necessarily think that undergraduate classes are easier content wise, I just think that by the time you get in grad school, you not only know what studying methods work best for you, you are studying something that you really enjoy, which makes any class easier in my opinion...