Possibly because at 11px Verdana renders nicely. I guess at the time he came up with the design, there was not really an alternative to use CoreFonts, and this

Possibly because at 11px Verdana renders nicely. I guess at the time he came up with the design, there was not really an alternative to use CoreFonts, and this was one of the types that rendered fine at that size. FWIW headings are in Gill at 17px, and I don't find the balance unpleasant.