Why aren’t random photo screensavers very random?

Windows has a built in screensaver that purports to show random photos from the My Pictures folder, and the Google Pack contains something similar. Neither seem to work very well, though. Google’s in particular seems to iterate through folders in a regular order, and despite having 10,000 photos I see the same shots on a regular basis – there are whole directories that are never touched. According to my parents the Microsoft version is the same.

I know that true random numbers aren’t really do-able by microprocessors. But there must be at least a faux system that’s appropriate in this case, surely? Google’s screensaver always shows me images from the root directory first – that can’t be the result of problems with random number selection. Are there any random photo screensavers out there that at least give the appearance of being random?