Okay guys, let me ask you this. If a table full of tight-aggressive players folds to the big blind, no matter how many players who are at the table, is the big blind more likely or less likely to have AA?

He would be more likely to have AA because those players are less likely to fold hands with aces in them. That means that hands that have aces in them will be disproportionately represented the times that the big blind is folded to, so AA will be more likely.

The answer is that the big blind's range is stronger in full ring than six-max in the scenario offered in the OP. The point of this is for players to wrap their heads around the idea that outside factors can change the strength of a range even if it stays the same.