There's no such entity as a "Bitcoin" that can choose whether or not to block or not S.DICE transactions.

Any blocking would be done by individual pools.  It would only take one large pool to actively be hostile to S.DICE to make them unable to allow zero-confirmation bets at all.  If a pool discards S.DICE transactions but intentionally allows competing transactions from same source to process then the pool only needs a few % of network power for anyone to profitably attack S.DICE by trying to double-spend any losing bets - the few % of times the pool includes the double-spend (and cancels the losing bet) then outweigh the house edge on the rest of bets.  You underestimate the extent to which some are opposed to S.DICE (not me - obviously).