I have liked Mr. Pink's theory from the getgo and I now think he is correct, those who can log in to the SW sib site are probably in. SW seems to have the most high class operation when it comes to the application process and their website, so I am thinking that those who have been accepted have gone into their system already and have access (ie to the big sib component), and those who did not match have not been given sed access. Of course this is speculation, but it seems to be quite founded.
As a test for your theory asiandoc, we can conduct an impromptu poll of those who ranked UTSW #1 and have access vs those that did so and do not. Actually, of those who ranked it 1 and have (close to or) above the UTSW averages (~3.80 and 32.5 I believe) would participate only, then it might be a little easier to determine the validity. Just a thought.