Also, Deb commented to me that showing "all bets profit" as -20 looks bad and will be off-putting to gamblers.
Better, she says, to show "site profit: 20".
I don't know if she's right, but she's usually pretty intuitive about such stuff.
Agreed. Telling gamblers others have lost X amount of bitcoins doesn't really encourage to play

But, what happens when gamblers start winning ? The Site Profit will show in -ve and investors will be discouraged !!! It can be kept in a logic I guess...
When Gamblers are winning => Bet Profit
When Gamblers are losing => Site Profit
True. But without players the investors won't earn anything.
Besides, investing is usually something you think about and thus you know the math is on your side in the long run.