Interesting discussion this one, and now that the crisis is over, I'll thrown in my 2c worth:
mella2007 was facing a couple of issues (at least a couple):
1) would they be allowed to check-in and board their flight leaving Oz - almost every response addressed this issue;
2) almost no-one addressed the question of whether, even if allowed to check-in and board, they'd be allowed to enter Thailand. The Thai immigration authorities are not going to rely completely on Virgin's judgement, they're going to make their own decision too. So this question actually needed to be answered too.
There's even the (slim) chance that they might had problems on the return trip, i.e. when checking in again in Thailand, getting in trouble for not having 6 months left on their passport. You can see how they might want to crack down on this, as otherwise it would be possible for someone to enter Thailand with 6 months left on their passport, but then change their flights so as to stay longer and beyond the validity of their passport, ending up stuck in Thailand which is presumably what Thai Immigration are trying to prevent happening!
Even if you are eventually allowed entry/exit, being grilled at immigration or check-in is not something you want on a holiday. I had an unpleasant passport/visa experience returning to Australia a year or so ago, and it made a very long flight quite nerve-wracking for me, as I wasn't 100% certain I'd be allowed to re-enter Australia (Irish Passport, Permanent Residency visa).
I'm glad mella2007 had no problems in the end, but it might have been worthwhile for people offering advice to actually have broken the question into its constituent parts, instead of just talking about the airline check-in procedures.
IP