The reason I would use Apple and not Linux is for the UI (though Gnome ad KDE are comming along nicely the NEXT component of OSX is the best UNIX UI out there. I dont need a UI for basic web services, but yes the system itself can do anything Linux/UNIX can do cause it it Unix... I for kicks set up OpenDarwin on a PC and tried to get KDE to look like osX but Im not a huge BSD guy..
Did PHP finally get their ISAPI filter nastiness worked out?