DDG's real issue is that they don't use their own indices. As far as I know, they are still dependent upon the Bing APIs in order to actually perform the search. So, while they have shown that there is a lot you can do (wikipedia integration, for example), there is a lot missing on the backend.
I remained woefully ignorant of DDG until Spring of this year (no clue how, I just missed it), but once discovering it, my definition of a good search tool has been forever changed by a single character.
The ! (bang).
!walmart, !netflix, !.net, !clojure, !java, ...
!weatherspark (huh, it's not there, I'll submit that, now anyone can !weatherspark)
The ! means DDG is my single-point search engine for almost any site imaginable. And it uses that site's search feature instead of a naive textual scrape (a la Google).