Just to nitpick:
- Focus on the one system.
- Fork the one system if it becomes crap.
Any contradiction there?
Let me pick your brain with this one: Standards. All the various Unix flavours support POSIX, OSS and X11. In a sense, *BSD, Solaris, AIX, HP-UX, AUX, Tru64, etc... are all united. They provide a better development environment since they all support the same software interfaces for scripts, system calls and multimedia.
On the other hand, Linux has diverged and continues to diverge from these common interfaces. You might say that Linux is harming this software union by introducing bash, Wayland, ALSA, V4L, etc... They're almost like an open source version of Microsoft (dare I say?). The irony in this is that Linux fans whine about following standards when it comes to Microsoft. But Linux developers themselves do not follow standards anymore (these snippets of code are generally called Linuxisms). To make things worse, when Linux developers work on FOSS, they propagate Linuxisms into everything they touch thereby ruining the portability of the projects.