First i would bet my house on it that SEOMoz is totally built from scratch.
Second - Of course is not hard coded i suppose there is a framework to ease the process of building stuff ex: Zend Framework.
A framework would make it easier and cleaner for building scalable website solutions.
Third - I don't think a website no matter what type it is needs all the vBulletin complete forum solution. I think you would need certain forum features as you want to connect a user though the entire website so he does not have to register 10 x times.
If your entire system (office) is .net i suggest create a common bridge ex: database and let the online stuff work with php ... and keep your system asp.
It's only my view. Again i can be wrong.
