This is not specific to Mac users. Most prefer applications which integrate with their desktop environment well. It's a tradeoff. Using something like Qt will try to mimic the native UI close enough, even if not 100%. But saves you the time on learning each native toolkit. I'd say it usually pays off, and that small percent doesn't worth the effort (especially if the project is supposed to be cross platform).

Who downvoted this guy and what for, when he's only stating his opinion on what tools to learn if one wants to develop for desktop?

And I personally think he's (shmerl) right. Learning a couple almost completely redundant APIs, but each with it's own problems, gothas and plain stupid decisions is hardly a good thing.

Years ago I would have agreed with you, now I'm not so sure.

Most users know so little about the UI of their computers that they don't know when to click the mouse once or twice.

They spend their day working on Windows, checkout Facebook on their iPhone on the way home, play a game on a Playstation then send some email using Gmail on Safari.

Then you have the major changes within operating systems over recent years, Windows Vista/7 and Windows 8 both introduced major UI changes as has OS/X.

Peoples interaction with computers has become much more diverse. Unless the UI is jarringly different they just aren't going to notice.