There are a few examples of this problem in action. Anime and Manga fans know how much back-story was missing in Akira, a long and extremely well scripted feature. On a more personal note, I cringe at ports of old TV shows to film. Let 'Charlie's Angels' be good. Anyway, the format problem combined with skyrocketing production costs creates another difficulty.
Comics can afford to put the burden of understanding on the audience.
Movies have to make everything plain and simple for everyone who buys a ticket. And it just isn't that funny forty-five minutes later, walking out of the theater. To please the largest audience and get the highest gross, everything must be explained, especially in the first film and so origins, rewritten to fit the film format, are always present. If anything X-Men proved that doing a comics movie right was ten times more important than doing it expensively. And any foray into another medium can guarantee itself fanboy support, a small but unequivocal revenue.