ingoditrust
My theory is that with high GMAT score the adcom sees you (high GMAT scorers) as someone applying to McCombs as a backup option and not a top choice. This might not be the case for every high gmat scorer on this forum or outside. By wait-listing they are just playing the waiting game to get a better idea if you are really interested in the school or not. I am not sure what the rules of wait-list for McCombs are but if you can show real interest by attending events etc or providing extra material (positive of-course) you might improve your chances.
I think this is partially true. McCombs is a little off of the beaten path location-wise for most MBAs, so I spent a lot of time researching the school and highlighting why McCombs was a program that I wanted to be a part of in my career essay. It was easier for me because I am looking at working in energy after getting my MBA and McCombs has a couple of interesting energy initiatives.
I'd think it would be really difficult for someone who wants to go into a more traditional consulting field to sell the AdCom on why McCombs is a great school for them, particularly if it seems like they have the profile of someone who'll be admitted at a higher ranked school. Schools want to think they're special, and don't like the idea of being someone's backup.