Sorry if this is a FAQ.
I can't speak for the designers, but there is a design pressure to keep the fork as short as practical. Fork blades, steerer and front triangle are all stronger if the crown/headset/downtube lug are lower. Headsets last longer too. None of these effects are large if we're talking a few millimeters, but I'm pointing out that there is a reason to keep it low, unlike in the rear where the height of the seatstay bridge doesn't affect frame strength at all.
Also, shorter reach brakes are usually stiffer, which is usually a good thing, and rear brakes aren't as important. So giving up some brake stiffness in the rear for easier fender mounting and better clearance for mud and bent wheels doesn't really cost anything, whereas it does have strength and stiffness costs in the front.
Of course the original designers may have had something completely different in mind!
Mark Bulgier
Seattle, Wa
USA