Also the only claim to us not being provably fair is the house doing transactions, you can check any of the hashes used. most the time its in the $1000s i have even seen a 1.2 million dollar transaction i don't think anyone is going to send 1.2 million USD to rig a game where you make $0.04 lol
But we see your point where even if it is not economically profitable, and extremely hard to do there still is that chance.
The monetary value of the transaction need not be large. As long as Blockchain.info accepts the transaction the attack could be performed with just a few satoshi as well.