Porting Pains

Yesterday and today, I've been porting my application to various UNIX platforms. I develop on Red Hat Linux Enterprise 4, on an dual amd64 machine. Everything works great on Linux. I also do some development on a Solaris 8/sparc machine, and pretty much everything works there as well. However, the entire produce supports other UNIX variants. Here's where I am with these.

Linux: 2.6/2.4 kernel - builds, links, works, yay!
Solaris: 2.8/sparc - builds, links, works, (slow)
HP-UX: 11.00, builds, links, (problems with named-pipes being implemented differently, plus some extra defines needed for POSIX compliance (socklen_t comes to mind)
AIX: 5.1, builds, doesn't link due to some goofy "-b" options that g++ really doesn't care for
OSF/TRU64: 5.1, build, links, but just you try and run, you'll see that libstdc++ is bad

Makefile conditionals, system dependant #ifdefs, differing library dependancies, it all just makes you want to cry. My question is, why doesn't everyone just use Linux?

A totally unrelated note: I just installed Ubuntu on my laptop, and it's pretty cool. Although I'll have to get used to a debian based distro vs a Redhat.