You speak as if every studio decision has been a good one! Which I would debate. But to your specific examples, comic Stark was kind of a lame ******. Movie version is an interesting, funny, charismatic ******. Improvement. Evans is, in fact, perfect as Cap. Renner is like Ultimates Hawkeye, which I can't stand, but they gave Iron Man the witty anti-establishment personality, so Hawkeye was left with being generic special ops guy. And McAvoy is just a younger version of Prof. X, who we didn't get much exposure to in the comics (that I've read--even in flashbacks in the early comics he's already fairly old and bald!), so I don't know that it's a great stretch to give him hair and to make him less stodgy. You would assume he wasn't an old, bald retiree his entire life. All the major Batmen in films since '89 have captured key components of his personality, but he's been written so differently over the years that he doesn't really have a core personality type, apart from being driven beyond the point of most men to protect the weak, and that he's gloomy.They do this with almost every character though, Downey is not the perfect Iron Man, Evan's is not the perfect Cap, Renner is nothing like Hawkeye, Mcavoy is absolutely nothing like the Professor X we know from the comics, same for Patrick Stewart, Michael Keaton, Christian Bale, Heath Ledger etc.....
Wolvie isn't complicated, but he's got some core personality characteristics that have made him appealing, and one of Marvel's top 2 or 3 guys for 20+ years. And movie version has become a watered down version of that. On one level, it makes sense that they did what they did, but at the same time, I was reading about comic Wolvie when I was 5-6 years old, and loved him. Others did, too. So I don't know if it would be so risky to make him a bit edgier in the next incarnation. Wouldn't surprise me if it actually had a positive payoff.