Any decent geek and Microsoft skilled admin knows Windows does (or has more than a "strong suspicion.")
Not necessarily back doors per se, just "features" that permit feds and such to snoop via various methods. While stuff like truecrypt, for windows, has some nasty holes, I wouldn't trust stuff like Microsoft Bitlocker as far as I can throw it. Reason? Simple, Microsoft is known for having already been in bed with the NSA/blackbag folks in the past, and when busted, they backpedaled about it and pretended it was just a joke by their programmers, in naming certain things. It was back when they introduced user/documents encryption in Windows XP. That's why all sorts of "police and law enforcement data recovery tools" were sold all over the place and the guys who sold that stuff made good money. Its like expensive, well made, hard to break into (without vandalizing them) cars to which the manufacturer still sells a master key, but only to the people you most wish to keep from surreptitiously searching or planting evidence in your fancy car. Same deal with MS OS's. I wager Windows 8 is laden with all sorts of bullshit.
Not so sure about Apple, and I wager with the right tinkering, one can reskin and retool Darwin BSD as they feel fit, that being the beauty of a unix-like kernel in the first place.
Linux and BSD have bugs, no argument there, but at least, the bugs get squashed promptly within time of being reported (there are some bugs that, for example, prevent a multiple processor or multiple core system from running without crashing but those are "fixed" by a competent administrator or dev knowing how to compile the kernel and what to put in and what to take out and how, and when.)