IWD was definitely reminiscent of BG, but not only did it use the same engine, it deliberately aimed for a similar gameplay experience, and was set in the exact same world, so there was no problem with that, either. If Fallout 3 was set in some other part of the elder scrolls world there wouldn't be much of an issue. But it's an entirely different setting in almost every imaginable way, and what's more, a history of very different games.
For example, if we developed IWD3 using the ME engine, could you blame people for not wanting it to feel just like Mass Effect?
I get the impression that the Bethesda devs honestly think there is potential / value in the level scaling system. I'm not sure of course, but that's the impression I get.
I was talking more about the main quest - where you have big demons and Diablo-like gates screaming WE R EVIL at you. Imagine if the Super Mutants vs. Brotherhood of Steel in FO3 adopted the same kind of symbols/discourse. I'd feel like I was in a bad American movie.