The problem is that "nice guys" generally try too hard to placate a woman to the point where I imagine it must become irritating and very vanilla for them. It's not that women like ****s (although this does sometimes appear to be the case), but yes, the strange "I can change him!" phenomenon is pretty prevalent in society.
To speak generally, I guess women probably want a nice guy who has a bit of a risky, cheeky edge to him to the point where it generates easy, spontaneous amusement. If a couple were simply posturing for each other and doing everything the other wants without any gentle teasing, things would just be incredibly boring I imagine.
I can speak from some experience, I guess. When I was young and naive several years ago, I attempted the whole "be nice as pie" thing - it doesn't work. It makes you look fawn-like and I guess, rather desperate. Go out there with a good opinion of yourself (although not to the point where it's flagrant egotism), and don't comprimise yourself to coincide with a woman - they'll probably respect you more if you have a dissenting opinion and are passionate enough to espouse it without fear of reprisals

(to put it bluntly, I argued the merits of Batman vs Spider-Man with a girl recently and didn't leave her room until the next morning, *ahem*

)
I am one to defend the concept of the "Friend Zone", and it is true that women can be utterly feckless a lot of the time, but then unfortunately, the societal onus is still on the male to be the one to "make the move" in most cases.
The problem with the attitude of many "nice guys" is that they think they're owed something by simply being nice, and I guess it's rather self-evident to women they're trying to "pull" and such. The best thing you can do is be comortable with yourself and try and work down this complex that women are just after ****ers all the time.
I know this worked for me - I really made a conscious effort to just disconnect my bad experiences with women (i.e. being passed over for someone I saw as entirely inferior, as condescending as that sounds), and it pays off. I've certainly done well for myself in the last year, and I guess it just manifests itself really. A positive attitude within is going to be displayed to everyone else

Hope that wasn't too long/pretentious. Cheers guys. I know where you're coming from, but I guess I'm something of a "nice guy convert" (whilst not becoming a douchebag), so I feel that I should speak on this matter as someone of a little experience.