Gearing, and the wheel size. Just easier to turn it over from dead stop IMHO.
As it is in the snow I'm runnin' 2.1 inch knobbies now, and glad for it.... whew what a dump we got.

I'm in a pretty low stretched out position on both bikes (actually a bit too long but... that's to remember when buying a NEW BIKE in 08. Both have a decent saddle to bar drop.