Hi quinquenion, I'm referring to the following excerpt on this page
3. You do not need official transcripts for the initial application. However, if you are shortlisted, we will ask you to mail (or have mailed for you) an official transcript from each college or university you have attended. The address for these transcripts will be:
Mathematics Academic Services, MIT Room 2-285 77 Massachusetts Ave Cambridge, MA 02139-4307 U.S.A.
The official transcripts will then be checked against the grades and courses you reported on your application.
So I don't think this is an "official transcripts required only if admitted" policy, as they could have simply said as much. Maybe I'm reading too much into it.