> My anecdotal experience is that I don't see porno comments or submissions from most reddit users either, but that's obviously skewed by the reddits I'm in.

I've moderated several web forums in the past, and the majority of spam porn pictures were hotlinked from reddit, so much that I had to ban reddit image links. You don't see porn submissions because the NSFW content access is disabled by default in reddit your account.

However reddit has absolutely no system in place to prevent porn pictures/videos to show up on other website apparently, when a simple cookie (or its absence) would prevent that content to be hotlinked anywhere else on the internet.