I agree that the "provable fairness" offered by services which change the server seed for every bet is very hard to take advantage of as a player.

If I play at PrimeDice, Bitzino, prcdice, and probably many more, for every roll I make I have to:

1) make a note of the server seed hash for this roll
2) pick a client seed in an unpredictable fashion
3) make the bet, noting the number they rolled
4) verify that the hash of the published server seed matches the one in step 1
5) verify that the published server seed combined with my chosen client seed gives the roll I saw in step 3

That's a LOT of work. Almost nobody is going to bother doing it, and so for all practical intents and purposes the site isn't provably fair for the majority of people.

Compare the above 5 steps *per roll* to what a player at Just-Dice or CoinRoll would have to do per roll:

3) make the bet, noting the number they rolled

That's right - they can just spam their bets, keeping a record of the rolled numbers.

That is because the bulk of the work required to verify PrimeDice rolls has been moved to the very start and very end of play, not per roll.

At Just-Dice, steps 1 and 2 are done before you start play, and steps 4 and 5 are done after you finish a session. You verify all your rolled numbers in bulk, using a single pair of seeds.

At CoinRoll, step 1 is the same for every player (the site has a global server seed per day), step 2 uses your most recent deposit's txid (obviously out of the site's control (unless they use transaction maleability, I guess?)), and steps 4 and 5 can only happen at the end of the 24 hour period.

I think JD's system is better than CoinRoll's, since it puts control entirely in the hands of the player. He gets to reveal his server seed whenever he wants to and doesn't have to wait until midnight. But both systems are vastly better for the player than having to do all that tedious work for every bet you want to make.