Counterpoint in favor of Apple:
Contributions to an open web: Open source development of Webkit and now Webkit2, HTML5 Canvas, Adverserial stance towards Flash in favor of HTML5 [iPad, iPhone]
Contributions to open-source tools: LLVM and CLang, MacRuby support, launchd, Cocoa bindings from other languages [possibly phased out?]
Contributions to open-source operating systems: OpenDarwin http://www.opensource.apple.com/
Developer ease: Nice set of installed developer applications, Development environment based on standard opensource toolchain, Compiling command-line tools from Linux/BSDs is sane and easy, Compiling X11 dependent apps is possible
Multi-platform support: BootCamp, The only system capable of running the three major desktop operating systems easily and legally.
High quality, hackable GUI environment and applications: Cocoa applications are generally built to a far higher standard than Linux GUI applications IMO, Cocoa applications are imminently hackable (see SIMBL)
Hardware innovation and quality: Forward thinking innovation in hardware: Mac Air, for example, gets rid of even ethernet!, MacBook Pro line widely acknowledged as top-tier development machine
[Disclosure: I have no stake in Apple.]