You completely miss the whole point of SatoshiDICE
Spamming the blockchain?
Heh, ... well that's a symptom.
What I was referring to is how SatoshiDICE is cheat-proof. (well, they could cheat and you might not be able to tell until the secret is revealed the next day, but by the next day you can know that your bets paid out or not because of math, not because the operator happened to be honest or not.)
There are ways of cheat-proofing without spamming the blockchain. The server could provide the hash of their secret, at which point the client inputs their secret. The two secrets are concatenated and hashed in whatever way satoshidice does it.