Desktops

I was reading a post from FTPOnline. There is a reference to Google’s Zeitgiest showing that Linux is only on 1% of the computers that accessed Google while Windows XP was at 51%. But the thing that I find most interesting is that 5% is given to the category of “Other”. Does that mean that Google could not identify 5% of the computers? Is there some browser that doesn't send OS information? Is it some application that is accessing Google in a way that Google cannot identify it? What is going on? 5% is quite a bit, it is a lot bigger then Linux and Mac combine.