Well, what's the point of an endorsement? To save you the trouble of researching everything yourself because someone who you already know tells you what they think. If you trust the endorser, then they've saved you some time. Ditto if you distrust them (there are some people that if they endorsed my favorite candidate, I'd probably be so suspicious I'd change my vote). I know a lot about what the xkcd guy is like than my senator (well, not my senator (Obama) but probably everyone else), so his endorsement is more useful information.

It was also a well written explanation of his views, whether you agree with it or not.