Wikipedia has historically dominated Google's search results - no one would argue with that.
But now with the knowledge graph, does Google have a need to rank Wikipedia at the top, when instead, it just takes the content from Wikipedia and other sources and places that information in the top knowledge graph box? The answer seems to be no.
A WebmasterWorld thread has webmasters and SEOs commenting that Wikipedia for many queries and search results no longer dominates. So I checked with SearchMetrics and there does seem to be a downward trend there:
Here is what one webmaster said in the forums, that before in the Google search results, the rankings were:
1. Wikipedia page
2. Big organization page
3. Government agency page
4. My page
Now they look more like this he said:
1. Big organization page
2. Government agency page
3. Wikipedia page
4. My page
I think the knowledge graph/quick answers has to do with it.
Forum discussion at WebmasterWorld.