also bitcointalk.org is earning $2,068,560 ~ 48.63 ~ BTC per year
That would be correct or ~ if bitcointalk was monetizing the forum with google ads. Since most of the visitors are from countries where CPC is quite higher, the estimated amount isn't too bad.
edit-
That's too low. I thought forum ads revenue was quite high as I didn't check closely ever. I was in the wrong thought that forum generates at least 0.10 BTC in an auction.