My guess is that there are a lot more "signature verification events" on Linux that pull from a deb or yum repository than there are on Windows servers, both because the mean server in terms of global usage seems to be Linux (though not the median, I'd think?) as well as because it seems like Linux folk rely an awful lot more on distribution repositories than Windows server users download things. Happy to be corrected if anyone has real numbers, though. My feelings are informed by my company's download statistics which may not be representative.