I think that the approach that DDG is taking is wrong. Relying upon individual sites search engines isn't going to lead to uniform results because they are always going to vary in quality.
DuckDuckGo won't ever be able to compete with Google as a general search engine. Google already pretty much solved that problem, and even if they haven't they have a huge head start and a much bigger bankroll. If DuckDuckGo is going to succeed on it's search principles it's going to be as a curated search engine. That's a game where they can still compete with Google.
I completely agree with you about the lack of uniformity in search results. Curation is hard. It requires that a good source exist, that the curators are aware of it, and that it's amenable to being added to your system (technically and legally). Only one of these is under the direct control of the curators.
The reason the Python search sucks in DuckDuckGo the people running the curated Python search have a crappy search engine. Obviously either a better choice doesn't exist (probable), the DuckDuckGo curators don't know about it (very likely), or the better source isn't technically or legally accessible to the DDG curators (unlikely but possible).
Unlike the problems of a crawling and building general search index (where even to enter the market you need to have a massive infrastructure investment), these smaller problems of curation are attackable by a smaller team with limited resources. To improve the search results for !python they won't need to re-engineer their entire crawl/index infrastructure, they will simply need to pick a better third-party source once they are aware of it existing.