I do think there's a lot more than we see here, or that any one person can see anywhere. I also agree that ad revenue doesn't really work without substantial traffic. Really, Reddit has usurped many traditional forums.

I tried to monetize an Android app with ads and a paid version. I could never gain enough users. I had a second app with more users, but didn't want to clutter it with ads. Of course that one actually had a decent number of users, but infrequent use (designed for utility, not monetization).