>Linux [...] managed to take over[...]. The question is still open if it was because of copyleft of if it was because of something else (Linus personality?), but it looks that copyleft actually helped.
With respect to Linux (both in the sense of kernel and as operating system bundles called distributions), "quality of implementation" is the reason for many a user. Lately with all the security agency crap going on, I would prospect that open source (just open, not necessarily free) would garner an increase in followers.