IMHO DDG's success stems from the fact that yegg listens to the users, is small yet big, and addresses a niche market - the one that demands quality results and settles for nothing less.

By being small DDG can address issues that others will not even think or bother thinking about i.e. enhanced privacy controls, TOR utilization etc.

I believe that Cull was a dream that went south. Unfortunately that dream had a hefty bill ($33m).

Strangely enough I visited that site once before and could not put a name to a site until I saw a screenshot of it.