Perhaps the answer is cultural. I think you will find that numbers play largely in far Eastern cultures, where numbers are attributed meaning (e.g., luck, success, etc).
That said, in Western culture, the "-" character in domains may be thought of as an "&", thus some might see a name like m-m.com as M&M (not owned by whom you might think, they own MMS.Com and M-Ms.Com - so they clearly see the - as an & character which probably helps in positioning the L-L characters value)
Makes one wonder how much the holders of M-M.Com would have wanted for their very old name.
In addition, the "-" character also is perceived as a word separator. So a name like T-A might be seen as a shortening of Tour-About or some such combination of words or even the ultimate vanity domain (short of an actual two letter .com) - a person's initials.
-Commerce