I also believe that ESPN prevented anyone from wearing online poker logo’s on their shirts/hats. If this is true, then PokerStars will not get the exposure that it did with Chris Moneymaker who won last years WSOP. He was wearing their hat and shirt throughout the event.
PartyPoker may not be the best poker site around, but they are a marketing machine. I promote them as well as Empire Poker (Party Poker skin) and I am doing extremely well. All the sites essentially provide the same service, it is just a matter of who markets better.
I also check the integrity of PartyPoker affiliate stats by having friends play and also creating dummy accounts to make sure they are not shaving, which they are not.
I make 90% of my Poker Affiliate income from Party + Empire poker.