It's crucial that they made fun of the PC, not PC users. (Remember, it was always "I'm a PC" in the intro.) In doing so, they clearly leveraged some stereotypes about the user base, but they avoided directly mocking the customers of either platform.

That said, I'm not sure this Microsoft campaign mocked anyone either. It didn't have any humor to it, and that's part of why it was such a lame effort. At least Apple's ads had a bit of self deprecation to them in how they depicted the Mac.