Actually it depends on the bet amount of the gambler. For a bet amount less than 0.001 BTC, a 0.0004 BTC flat deduction is huge. But, for high rollers, it does not matter, because they are enjoying the 0% house edge, which is a privilege they wont get anywhere else. I can foresee that in future chain-bet.com may turn into a temple for high rollers.
Just for everyone too lazy to do the maths, if you are betting > 0.04 BTC per bet, this site offers better odds. If you're betting less than that, you're better off playing a traditional 1% casino.
Although personally I'd be too skeptical to play here. The site is trivial for a miner to profitably (and undetectably) cheat... (and even more so for a mining pool, which can cheat it's miners at the same time if they have to discard a block)