My 60 BTC is then exactly 6% of the bankroll, and the owners' 200 BTC is 20% of it.
Then, if someone deposits 1 BTC onto the site, bets, and loses it, that 1 BTC gets split up to all the investors.
I get 6% of it - that's 0.06 BTC. The owners get 20% of it, or 0.2 BTC, and so on.
if dicebitco.in works similar like just-dice I think your math is wrong, because there is a 10 % fee on investment profits.
(probably in order to pay for hosting, security and so on)
Nothing wrong with those maths.
But when investor divest some of his profit 10% of it will go to site owner.
And JD took 10% too so there is no difference.