Mac OS X is Unix-based, so it follows strictly all the industry standards, so the syntax and operation of any cross-plataform language remains the same as in an Unix workstation (or a Linux box) or windows.
Maybe you still have the idea of the idiosincracies Java-developing in Mac OS pre-X had, but not anymore. Personally I have tried some C-code developed for Unix (SUN) and tested some shell scripts in Mac OS X, they executed without problems.
As far as I know, PHP and Javascript are scripting languages and they need a web browser to run. The default browser for Mac is called Safari and it follows very well the W3C standars, anyway, you can use Firefox, Chrome, Opera and a miriad other browsers (except IE, MS itself said Safari is better adapted to Mac).
I'm not very web knowledgeable, but as Mac OS X is pretty much standarized, don't think it has any web services lacks. Hey, you can even install and use Apache and Tomcat!
