Why will anyone still play SatoshiDice?
Gamblers will pay a premium to play on a trusted, reputable site that has a long history of not defrauding its customers.

As noted by LocalBitcoins, Betcoin is accused of shady behavior, including lying about their trademark, failing to correctly use a provably fair system, playing on their own site to inflate volume, and DDoSing competitors. Source: http://bitcoinmagazine.com/7659/betcoin-tm-allegedly-fraudulent-activity/