JerNYC: [..] open invites, it's always the same two people. [..] I get the feeling on BK that players are very protective of their ratings and not really willing to defend them openly. Or, I think they only want to play people of a much lower skill level so they know there's no risk for them.

It may be that one or two high rated players are setting rating limits in their open invitations but it's unlikely that many are doing so. It's certainly necessary for high-rated platers in games of chance such as backgammon but there it's about avoiding the low-rated players because they have luck on their side (ratings-wise, not playing-wise).

More likely is that high-rated players simply do not create open invitations, just like middle and low rated players don't create invitations. It's just not most people's style of game creation.

However, you can test your theory about hidden invitations by going to the WaitingGames page, logging out, going back to WaitingGames and refreshing the page. You'll see it in window-shopping mode, that is, you'll be a guest who can look but not touch. As such, you get to see all the goodies that you can't see as a logged in player. If there's no difference then there are no games with limits or made by players who you have blocked or vice-versa..