The true successor would have been torchlight people's working back at blizzard, along with their writers, the huge resources, the right to use diablo's material etc. Right now the guys at torchlight have to fight a losing battle, since blizz can simple throw more money and make a better product. In the end though, the true losers are we, the customers, who end up with two "good" games instead of one excellent.
It's like Fallout 3. Neither bethesda nor today's interplay was able to make it. Thus we got a butchered down version of fo1/2.