GNOME, KDE, etc, are not my choice of UI... I'd much rather start out with a minimal system, and add the software I need/want instead of being forced to use a system with a preset applications suite containing all manner of software which I'll rarely, or never, use. Of course the developer of a marginalized UI will see doom and gloom in Linux' future, but I consider such views to be an artifact of perspective, especially since the Linux userbase is continuing to grow. The fragmentation of the Linux systems is one of the reasons why I now use FreeBSD, and it's minimalist approach is exactly what I've been looking for over the past few years. I don't really see how competition comes into play when comparing free, open source, software with proprietary systems such as OS X (certified Unix product) and Windows.
These proprietary systems are mostly focused on profits, while Linux and BSD systems are (mostly) focused on stability and security.