Maybe so, but it's still gonna stick out like a sore thumb everywhere. Meaning annoyed users, meaning the app is never ever gonna become a buzz on blogs and shit, meaning low earnings.

I have a counterexample which comes immediately to mind, but he wouldn't appreciate being mentioned. So, trust me on this one: uses QT, well-beloved by a traditionally underserved market, is "a buzz on blogs and shit" for that community, now has a boatloat of competitors, and doing "quite well indeed."

Does last.fm's desktop client stick out like a sore thumb everywhere?

On a Mac it sure does.

QT has a style system that can closely match the target platform.

So does Java Swing, but that never stopped Java from sticking out like a sore thumb everywhere.

Users become very sensitive to the details of the windowing system, and when a program breaks their expectations, they often consciously recognize what's wrong with the program, they just get frustrated. I'm thinking of things as subtle as whether you can create and rename folders from within a Save As... box, or what the tab order of fields in a dialog is, or what cursor shows up when you drag & drop items. It's very easy to get the look & feel 99% right and still have users feel that something is still very wrong with the app.

Maybe just a bad example, but the QT doc says:

  On Windows, Mac OS X, KDE and GNOME, these static functions will call the native file dialog when possible.

http://doc.trolltech.com/4.7/qfiledialog.html

QT is way better than Swing. It's a laughable comparison, really. QT does such a better job at being native.