I picked up a copy of Fallout 3 yesterday.
This is going to really cut into my productivity.
When I heard that the developers had changed, I was a little worried that the tone of the game wouldn't be quite the same under the new team. The 50s-style post-apocalyptic future that wasn't is what really appealed to me in the series. I needn't have worried. From what I've seen, they've nailed it... and they've done so while converting the game to 3-D with a different perspective (and truly gorgeous graphics), a somewhat different combat system, and some subtle tweaks to the underlying game mechanics.
Then I look at D&D, and I wonder why they couldn't have done the same thing.
The answer is pretty clear to me. There was a demand for Fallout 3. Fallout 2 has limited replay value. That doesn't carry over into D&D. Wizards created most of the demand for 4e (think about their negativity about 3.5 over the past year or so) - as far as I can tell, most people playing 3.5 were fairly happy with it. If Wizards had made 4e a slightly shinier version of 3.5 with a couple of major changes (but, at its base, the same game), would people have given up their investment in 3.5 and switched?
It almost certainly wouldn't have been a rousing financial success for WotC, though.