Most games back then didn't take very long to make (compared to now, that is), due to the lack of complexity. Newer games take way longer. Also, blizzard has a MUCH different and larger team for all of their games now so the time it takes to make Diablo 3 will not be anything like what it was for D2...
Why would it take that long even? They have the game up and running. I've seen the videos. The fact that they actually have videos of gameplay instead of just screenshots or concept art is very promising. I would like to believe that it'll be out sometime at the beginning of next year.
"Here's to the Black Man....thanks for taking it all in stride" - Stewart Gilligan Griffin.
they have the game "up and running" because they've been working on getting it to work for the past four years and making a basic level and characters to show off
now they have to make areas, story sequences, record dialog, and pretty much everything else
this probably won't be out until summer 2009 AT LEAST
considering it's been confirmed that we won't see SC2 this year and that game was announced over a year ago, I think it's safe to say D2 will be similar, probably not even summer 2009 more like Xmas 2009