Well, I said it wasn't a perfect system. I certainly don't think it's fair to sell out every ticket via presales. As you said, that's not really giving the casual fan a fighting chance.
And while I don't really want this to devolve into a "who deserves tickets" argument, I'd have to say the folks who scavenge websites about their favorite bands, are on their mailing lists, frequent their chat rooms, or whatever, probably should be able to get first crack at tickets. At least those folks have an obvious interest in seeing the band. Since there's no official "I'm a big fan" registry, presales are a decent solution.