I think this discussion sidelines the question of whereone studies a particular major. I assume that a degree in political science means something slightly different at Harvard or Yale than it does at a public state university. Similarly, a degree in economics that emphasizes stats and math and analytical skills is quite different from one that takes a political economy approach. I think the most difficult class I have had as an undergrad was Latin, and that was largely a function of grading, professor's expectations and the material covered, which was significantly more than other foreign language classes. I have not had a single Thai session that has come close to the level of difficulty I had in Latin class, and this damn thing involves a separate alphabet.
As far as the relative difficulty of political science...I think it depends a great deal on the choice of classes, professors and emphasis. My major is a combination of political science, political philosophy and economics...which I thought made for a good pre-law combination. It also helped quite a bit when I decided to go abroad to study development.
That being said, I think my major was relatively easy. Now, it involved far too much reading...but I also had a good time, socially that is. I think that is possible with a variety of majors...even my friends studying physiology consider it relatively easy, bitching mostly about their chemistry classes. It depends a great deal on what you put into it, as far as course selection, and what your natural strengths are.