This forum is mainly for discussion of bitcoin and altcoin related topics. It's just only for bitcoin alone.
These two sentences of yours are contradictory. If the forum is meant to discuss bitcoin and altcoins, then it can't be for bitcoin alone. You are missing a "not" in the second sentence.
It's like Google, they don't care what ads being showed as long as you getting paid, why should it be different here?
You are wrong. I remember that 1xbit had ads on the forum a few months ago. theymos probably didn't know about their reputation when he handed them some ad space. Someone created a thread how that casino shouldn't be advertised here due to various threads showing their scams, so theymos refunded the money they paid for the ad space and deleted the ads.
I don't mind seeing altcoin ads on the forum, but I do find it peculiar that the forum allows that type of advertising considering how strict they are regarding altcoin giveaways. If someone created a Litecoin giveaway, he would be temp banned together with all users who participated on the grounds of incentivized posting. But the same person can rent out ad space and advertise a project in that way.