Wrong. Linux is the kernel. Just the kernel and nothing more. Little companies producing pretty useless programms with lots of ads just haven't discovered Linux as a platform.

I can't look at the source code of any linux app (borlands kylix for example) nor is there always a open-source version available. - Basically it would be possible to create commercial versions of Linux, sth like a Microsoft Linux (Windows XP is based on a BSD kernel which is more or less a linux-cousin).

As long linux has got a small market-share, companies sometimes give linux versions of their software away for free, but if that ever changed (for example if linux had a market-share of 10% of the desktops), they would consider making money with linux products and they would also write adware/spyware for linux.