Well, the only real difference I see between D&D and Shadowrun is the sets of dice used. And some of the mechanics are different.
I mean, d20 Modern has more of a cyberpunk feel to it, but at the same time, I like that in a d20 game, you have the chance to be a hero. When's the last time a shaodwrunner went back for that teammate that had fallen under a hail of gunfire? When't he last time they actually survived?
I know that d20 isn't as realistic as Shadowrun (at least, not as realistic as 3rd Edition... I have my doubts about the realism of 4th Edition), but it doesn't have to be. D&D is based on Tolkien, and d20 games are thier modern counterparts (so, for a zombie campaign, I would prefer to use d20 modern instead of Shadowrun, even though I usually prefer to play Shadowrun.)
Of course, you play Warhammer, and that's not really my thing, either. I just think it might be which you were exposed to first. Like whether WoD is biting on FASA, or the other way around...
-kv