Ok it is about plate form independent as Google Earth. Silverlight works on a mac. I do not know about linux has I do not have linux installed on any of my computers
Nevermind Linux, what about Free/Open/NetBSD, Solaris 10/OpenSolaris, Android, iPhoneOS, Blackberry, PS3, Wii, HP-UX, AIX, Haiku (BeOS), Symbian, Maemo ...
The list goes on. This is the difference between open standards and proprietary. With open standards, every vendor is free to implement the technology. With proprietary stuff, we'd need MS to port their silverlight crap to all these OSes. Guess what ? Not happening (heck, even Adobe doesn't support all of them for Flash, and they have more reasons to).
Everyone of those platforms has a browser with HTML/DOM/CSS support because those are published standards they can implement.