Why do people play satoshidice?
The odds are 98%.. so if you start with 1 BTC you should expect to end up with 0.98 BTC..
98.1% and when they started out they were 98.5%.
Odds at a vegas casino for slot machines, etc, are much lower, maybe 96% and down, even 92%.
State run lotteries payout about in the 70% range or less.
Blackjack at a casino table might have better odds, depending on how you play and how many hands.
Now because what SatoshiDICE does can be relatively easily replicated, a competitor will probably undercut SatoshiDICE by offering better odds, maybe 99%. An ad-supported service might even be able to beat that, giving even higher odds.
But for now, SatoshiDICE provides something of value (a way to gamble knowing you won't get cheated, and without paying the house a ton for the privilege of *usually* giving them your money).