So... what made this Trios event more "casual" than normal tournaments?
In team events players can place blame and have to rely on others. If for no other reason this tends to make the event feel more casual.
Trios takes this up a notch. Half of your teams score in each round is completely out of your hands. Knowing this might help reinforce "Well I don't HAVE to..." and "Ehh, it might not matter THAT much..." lines of thinking. Players (should) know that as an individual they can not win (or lose) the event for their team. I believe this promotes the awesome, "Well it might be cool if..." mentality moreso than any other event. Sometimes people "trying different stuff" happens, sometimes it doesn't. All we can do is give people an environment that encourages it in subtle ways (like giving them two teammates, a weird point total, and a handicapped force org). I think Trios is the closest we've come to that.
For instance, the winning team had one player field an army he's never played before (in an event anyways).
I think overall the lists for Trios are a lot more "casual" than any other event.
I think it's very easy for someone to argue the complete opposite, but I don't think that holds true just yet.
The availability of the rules are just as to get as the codecies since BG can get the rule books.
This is only half true. We can not get all of the IA stuff. For instance, IA Second Edition is not available through GW.