Zed's very no-nonsense. He's spent a lot of time manufacturing an image of himself. He lets himself get carried away and angry and he's been searching for a community he likes, butting heads all the way.
_why, on the other hand, was truly bizarre. I never got into his blog, for instance, because it seemed frequently nonsensical and more than a little rambling. Despite that (or, more likely, because of it), he seemed almost always happy with whatever it was he did. I only ever really got into TryRuby and his Poignant Guide, but they were the only two guides to programming I've played with. There was a giddiness in his work that I haven't found in other coding. It's comparable to the moods of artists in other fields.
Zed's argument against _why is that what he did was impractical and unproductive. That's what made _why as a persona, though: Zed is a hacker, _why was more of an artist, pretenses and unreliability and all. It's left-brained versus right-brained; it's also why there's a definite rift between the people who like _why and the people who think the guy was raving mad and immature.