This is most likely that Google has more user behavior data than DDG. If enough people use DDG and click on the StackExchange link for that query (or similar queries), DDG will be able to get that to the top.
On the other hand, did DDG just use Bing API, and only Blekko crawls the web? Or do I get my search engines mixed up?
Personally I don't, but it should be noted that there are other indexes besides what you have mentioned. That said Samuru and Procog are pretty interesting.
On the other hand, did DDG just use Bing API, and only Blekko crawls the web? Or do I get my search engines mixed up?