This isn't really an accusation that PrimeDice is cheating. Just that their system is a bit flawed. More that we can't know by default if results are fair unless one changes his own seed for every roll. It can be provably fair, but only in that specific circumstance. A provably fair system shouldn't have a cheating possibility under any scenario, regardless of if the site cheats or not.
PrimeDice: changes secret every roll - makes the user have to do much work to verify (too hot)
CoinRoll: changes secret once per day - makes the user wait too long to verify (too cold)
Just-Dice: changes secret when the user asks to change it (just right)
Dooglus, I don't think Coinroll is "too cold". Doesn't JD provides a default client seed too? Need to change client seed once, good to go forever. Much better.
Fixed daily secret for everyone seems good. It makes it pretty much impossible to cheat players under any circumstances. Most people don't need to verify and won't do it immediately after betting or won't do it at all. The daily secret cannot be be changed without altering all previous bets for that day. Finding a secret that match all bets for the day would simply be impossible. We also don't provide a default client seed, avoiding any possible claim we chose one with lucky numbers favorable to the house for the current day/server secret. We simply use the user's deposit tx ID. Put simply, Coinroll users don't need to do anything to be on the safe side and we don't have to provide a default secret.
The whole point is everyone don't need to even verify and often most people won't. So archived bets are provided (not simply one by one bet lookup on the website, downlaodble archives for easy checking with script). Pretty much anyone can just run a check on the archives and report anything suspicious. When people are playing, they want results instantly. Verifying bet timing isn't as important. If you want to check that, you can always check bets in batch later. Being able to verify them immediately wouldn't change their loss/win. No new information. Just not as time sensitive, unlike betting which needs to be instant, so Coinroll use that system. Just seems like a stronger provably fair system. We have yet to see any demand for instant verification.