Mac OS X is UNIX alright, but to pull most of libraries from MacPorts is the only sane way to manage dependencies.
If you run Tiger (and see no reasons to upgrade) - then you are stuck with old Java release for ever. There is no way to upgrade Java other than buying Leopard, and then you are still at Apple's mercy for future upgrades.
A simple task like doing 'sudo emacs' requires some custom shell scripting, since emacs that came with the operating system is old and useless.
My initial excitement about Mac hardware is also dented after battery and graphic card both failed only after a year on my MacBook Pro.
A web developer would be much more happy on Linux if he/she could live without eye candy.