Most webcomics are one man/woman projects. One person writes the story and jokes. One person draws the strip. One person colors it and posts it on the internet.
It takes a special kind of person to be able to do all those thing really well. Sadly, I'm not amongst them, I can't draw for crap. I'd love to do a webcomic myself, I have a great idea, several of them, but my lack of artistic skills renders that plan moot. So what are people like me to do? Find a partner to do what we cannot.
And it usually doesn't work.
That's not to say it never works, it has. Parking Lot is Full was a team comic, as was Terror Island and Life of Riley. Of those that still update, Brat-halla (which has THREE people working on it), Shadowgirls, Punch n' Pie, Footloose, Our Time in Eden and Cyanide and Happieness all have two people plugging away at them. I'm sure I even missed a few.
But these seem more exceptions rather than the rule. Typically two people working on a webcomic will more likely cause the comic to fail, or the team will break up before it ends and change the very dynamic of the strip.
Megatoyko is probably the best example of this, the separation of the real Piro and Largo (and I really don't know or care what their real names are) changed the tone of the comic in an obvious and dramatic way, eventually leading me to stop reading it.
9th Elsewhere, a comic I still think of as Megatoyko by girls, had the same sort of breakdown, the fun element that had driven the comic up to that point vanished with the second person and while it was still good, it wasn't as good as it had been. And then it died of Hiatus.
One comic that SHOULD have worked was Metrophor, done by a brother/sister team. Sadly the sister part of this pair came down with a serious hand injury. And she was the artist. Comic is effectively dead now.
Marilth, the sequel to Krakow 2.0, went through several artists, including one that did very little at all, before finally getting one that could finish the story.
Successful teams usually are people who are physically close (they live in the same town), have similar senses of style and humor and are able to deal with each other in a civilized manner (which makes me wonder why I said Metrophor should have worked, siblings after all). Finding that is HARD though, and led to several comics just folding. PLiF died because of distance, Megatoyko's issues came from personality conflicts, and Marilith's problems were just terrible.
So yeah, it looks like there are many more successful pairs comics than failures, but I haven't reviewed every comic out there (and I only include the ones I read for these articles). The pitfalls are more numerous, and it's amazing that so any survive, let alone be successful. Still, of those successes, the comics that are done by one person alone are often far more successful and better done.
As much as I would love to write a comic, I'm a bit of a control freak when it comes to my story and vision and I'm sure it would fail utterly. Still, it's nice to dream about it, even if I know the dream is doomed.