Ethercrash used to have a 1% social bonus prior to it being reduced to 0.5%
This is why the current stats reflect that the house has paid more than 0.5% out in bonuses.
Well, that's reasonable. But still there are great problems with margin.
So looks like 0.75% is an average house edge between previous average house edge (0.5%) and current average house edge (1%). Clever manipulation.