I thought Steven made a very interesting and insightful statement when he noted that the dichotomies between the comics and film version of a property in many US adaptations are often great enough to induce dissonance, and that the success of many Japanese works (such as Naruto) may be partially attributed to the much rarer occurance of the same...
That is to say, if you watch Naruto on TV and then go buy Naruto the manga, you get more of the same thing, only better. Whereas if you enjoy the Justice League cartoon and go to buy a Justice League comic, you're going to end up with two very different things.
Partly I think this is due to the relatively smooth clockwork of media development in Japan, but I've also been given to understand that in the US adaptations are purposefully changed in significant ways because the developers want separate products. If the movie studio makes enough changes to Batman so that the movie version of the Batman is recognizably different from the comics version, then the movie studio actually owns a portion of their version, separated entirely from the original. They can then demand a greater share of profits generated by the merchandising of the movie version media, continue to make changes to continuity without concern for other iterations of the same IP, and so forth.
Considering that the people in charge of development have incentive to make changes, even if they're foolish ones, just to consolidate a greater percentage of ownership, I can see why getting any "faithful" adaptation of a Western comic is a difficult proposition.