There is definitely a hunger in the Linux community for quality commercial applications in areas where open source has not traditionally managed to perform so well (Image/Video editing, games etc).

You would certainly have limited luck trying sell a C compiler or package manager to Linux users for sure, but there are certainly areas (including some developer tools)where there could be a market.

If you released (say) an image editor for Windows and Mac you are competing with Photoshop as well as countless other programs, whereas if you release for Linux you may have less potential users (although there are still an estimated 30 million) but you are competing with The Gimp.

There is a subset of Linux users who would never consider any commercial software, but this is pretty small percentage, at least that is certainly what Valve is banking on.

Mac users do expect to pay for software sure, but Windows users? Not so much since Windows seems to be the platform with the highest piracy as well as countless horrible "freeware" programs.