Since you asked

This kind of tantrum has been a recurring punctuation-mark to Moore's brilliant career. This particular iteration is getting a lot of play because of all the movies being made from Moore's work lately, and because of the increased mainstream interest in comics, but to seasoned Moore-watchers it's business as usual.

Around 1987, flush with the success of Watchmen, Moore quit DC (along with fellow stars Frank Miller, Howard Chaykin, and Marv Wolfman) when the company announced plans for a ratings system similar to the movie industry's. The ratings scheme never happened, and Miller, Chaykin, and Wolfman are all still working for DC two decades on, but Moore stayed away. He later told the Comics Journal that "the last straw" had come when a DC editor threatened to launch a Watchmen spinoff series. (No such series was ever published.) Now he's accusing the company of tricking him into signing away his rights to V for Vendetta.

He's had a similar series of squabbles with Marvel over the use of the name Marvelman (eventually published by Eclipse under the name Miracleman, now sadly out of print), over Marvel publishing strips he did for the U.K.'s Dr. Who Weekly, over a credit that was omitted from a Captain Britain trade paperback. His involvement with the film industry is the same story again: interpreting 20th Century Fox's decision to settle a plagiarism lawsuit as a personal slight, demanding an apology for Joel Silver's Hollywood bullshit, etc. etc.

It's not that he's in the wrong on any of this stuff, particularly -- it's just that it happens so much you have to assume he enjoys it.

It's a shame, because I think all this antagonism has deformed his career. Imagine if, instead of bouncing from publisher to publisher, he had followed a path through mainstream comics like that of Grant Morrison, who has alternated periods writing mainstream superhero books (New X-Men, JLA, and soon Batman) with work on his own creations for DC's mature-readers imprint Vertigo (The Invisibles, The Filth, We3 -- all of which Morrison owns outright). Imagine if, instead of writing Superman homages in Supreme and Tom Strong, Moore had spent a year writing Superman, or if, instead of WildCATs, he'd taken over JLA. I suspect Moore's later work would be more satisfying, and mainstream comics would certainly be richer for his involvement. As it is, his most influential work was done 20 years ago.