I was, obviously I hope, just joking when I suggested that is how Mr. 'stad gets his ideas, but Bobby makes good points I wonder how long it will take for something like that to happen to a webcomic.
Sadly the first Webcomic it's most likely to happen to WOULD be Achewood, for several reasons:
1) Most Webcomic authors are so obsessed with people liking them that they will bend over backwards at the slightest hint of discontent from the audience. This is why most Webcomics are crap (you can't please everyone). Onstad is not obsessed with people liking him, or even people liking all of his work all of the time. At the core of it he is a businessman and wants to make a solid product that stands on its own merits for most people most of the time.
2) Most Webcomics are either here-today, gone-tomorrow, or have little if any readership. Achewood has enough market penetration that it's verging on the mainstream (Dave Barry likes Achewood, for example), and while it may never be a multimedia empire, it's still going to attract more attention than "Squirtz N' Kat" (a perky webcomic about a lesbian fox and a gamer geek living in Brooklyn, hosted on Keenspot, that I just made up)
3) Onstad pushes some people's buttons very well and those people would have a personal vendetta against him.
4) The concept of "fair use" and the extent of copyright isn't as well defined for Internet media as it is for paper media. This really isn't a reason why Achewood would be a target over other Webcomics per se, but it is something to consider especially given that the free product (Web comic) is repackaged, value added and sold as a hard product (Achewood compilations, for example.) Other Web comics that do that (the insufferably unfunny User Friendly, for example) tend to have large publishers backing them (in the case of User Friendly, O'Reilly), whereas I am led to understand that Achewood is more of a home grown thing.
I think about these things a bit too much.