Was to be expected to happen right? I mean, in countries where gambling is illegal, bitcoin offers the perfect solution without any direct traces to your fiat accounts.
What I like most though, is the possibility for relatively trustless betting (e.g. you send coins to an address for a bet), where you don't even need to have an account at a certain website (yeah, it is gonna be slower though).
Also deposits and payments, expecially for large amounts, are much easier than with fiat as hardly any verificications are required.
Plus, no more tax! It's waaaay easier to gamble online using bitcoin instead of going to the casino, turning the money to chips, placing the bet, turning the money back, just to lose the money [most likely] and going back home. Why do that, when you can do it in the ease of your bedroom? It's so easy, and you can choose what game you want to do, nearly instantly. Why wouldn't you do online gambling?
The thing about gambling being illegal in some countries also incentivizes online gambling with bitcoin, and its pseudoanonymity.