i think that wyogal is on the right track.
looking the pics, i'd guess that you baked it in a very well-greased, very dark pan, using butter, very close to the botom of your oven.
bottom of the oven speaks for itself. dark pans absorb & conduct more heat than shiney pans. lots of shortening also transfers more heat, and the milk solids in butter brown at high temps.
if you happened to have a dusting of flour on the top surface, that would also retard browning.
it's been ages since i've used an electric oven, so i may be wrong, but i think i recall that you can have the bottom element only, top only, or both elements on. if you where using only the bottom element, that would definitely leave the top unbrowned.
by the way, the loaf looks pretty good anyway.