Looking for Microsoft explanations for the specific file extensions in the SP blocked file extension list

We know how to add or remove extensions from the Central Admin blocked file type list.

What we have found, however, is that apparently that block didn't work so well under MOSS 2007, because files with extensions on the blocked list on 2007 still were able to be uploaded and downloaded.

Now that we have moved to SP 2010, this "hole" appears plugged - but that leaves us:

a) with files on the SP farm that can no longer be downloaded or updated

b) with requests to remove the block so that they can download or upload files of that type.

I would love to find Microsoft reference material explaining the _why_ for the extensions chosen - for instance, I don't see .mov, .wav, .wmv, etc. listed so size or streaming isn't the base issue I am guessing.

While security concerns _might_ be at the heart, if a site has a good anti-virus policy at hand, then reducing the number of types blocked probably is not too bad.

I just don't have a good idea what the reasoning is for the specific set provided, nor of their "best practices" related to the topic, and need that information to be better educated on the topic.

Has anyone pointers to official documents, blogs, etc.?