I tend to think of backlighting as falling into the same category as keycaps with fancy printing methods...
I mean, if you think about it from a purely functional perspective, for a touch typist, why would it matter if the lettering on some of the keys wears off? The argument, "you shouldn't be looking at your keyboard anyway" applies just as well to the case of pad printing vs dyesub as to backlit vs non-backlit. But some people care about the look of their keyboard, and their taste requires consistent lettering across the keyboard, so they spend the extra money on nicer keycaps. By the same token, some people have a preference for the appearance of backlit keyboards, and are willing to accept the costs to have that look. And that's really all there is to it.