Open Source does not mean Free-Software. The free in open source is limited to freedom. Freedom of reading, modifying and reusing the code.
OSS is Open Source Software and it can be a paid product too, and under GPL you only have to ensure that, for a premium fee or some other way, a user can download the source code. And any derivative works, if released commercially, must provide atleast the open-parts (the derived parts) of it under GPL.
FOSS is Free and Open Source Software which requires you to make your product free for use and free for downloading the source too.
Its a great philosophy even for enterprises, where in they can reuse well developed open source code to suit their inter-organizational needs for almost-zero-cost.
Commercial software will always continue to exist, but with free alternatives getting better and better, they will have to elevate the focus on quality and support provided - which does lack in community-powered solutions. Its not much of a threat.
@Charan - Cool down man, many don't know what OSS really stands for.