Good point. I was thinking that in (1) there are 6 ways you can be dealt A9, whereas in (2) there are 3 ways you can be dealt AA. (In both cases there is only 1 way your opponent can be dealt his hand once yours has been assigned.) But from the perspective of # of possible hands your opponent can hold to beat you once your hand and the flop has been dealt, you're right they are equivalent.

Also, from likelihood of the hands being played, scenario (1) is much more likely to happen than (2) since AAxx will get played much more frequently than 99xx. I guess I'm saying there is good reason to fear (1) more than (2).