That is weird, because Party’s financial reports show that they nearly doubled their revenue and per player earn by adding blackjack. My guess would be that maybe players are just playing less at party these days Professor?
Most players have a finite amount of spare cash to spend and time to spend it in. There will only ever be roughly the same amount of $$$ per player available to be raked at a poker table or won via a casino game.
I think that you should earn a little more with casino games available as it will simply encourage players to spend a little extra, more quickly as Party Poker’s published results show. And the good players will probably still rake just as much, but not withdraw as much as they lose a portion to the casino games. That means more % for affiliates.
If you were making less, it would also mean the casino is making less – so why would they keep the games? The earn per player in casinos is much higher than poker rooms, and there is no reason to think that the combination of games would earn you less together than either on their own.
I know that I always get sucked in and lose a little of my poker winnings playing blackjack at playtech rooms, party and paradise.