Yet this action does seem like collusion which was the oringal point. I didn't know transactions could be excluded as well. Who's to say that in the future miners could collude against certain merchants?
Oh they could if they wanted, and if they knew what the addresses in use by the merchant were. This could be made difficult by the merchant continually generating new addresses. The merchant could also add a little sweetener (transaction fee), and it feels pretty likely that a proportion of the wider BTC community would overcome their (presumably) ethical concerns and process the transactions anyway.
But yes, in principle, colluding miners could make life difficult for merchants they dislike. This is one reason why a large and divers base of miners is important to the BTC system.
The way the system is designed to deal with discriminating miners is to allow all discrimination (a miner can choose which txns to include based on any criteria he/she wishes), but diluting their choices by having enough miners.
SatoshiDice is actually very useful for the network, because it allows us to test how it functions in a saturated environment long enough in advance that we can make changes if they are needed.