I rather like Randy's current approach, which is that DOs need to be cross-referenced in community in order to make them as inclusive as possible. I'm personally comfortable with discussion taking place within a given community, but I do think that a gathering planned on Flyertalk needs to be made open to FTers generally. And to do that a notice in community is appropriate.
That said, I recognize that when a travel provider is picking up the tab and hosting, such as the DOs that CO has hosted, and especially when numbers need to be cut off or limited, they may have a strong interest in ensuring that their best customers are given priority. And on the whole I think that's ok. He who pays the bill calls the tune, as it were.
At least that's my take as a starting point, but am open to being persuaded that either piece of the approach is problematic.