Why not use Google? Searching for 'coverage.py', the bitbucked repository is the fifth link for me. The first and second link are more general informational pages which link to the bitbucket repository. Searching for 'coverage.py source repository' gives the bitbucket repository as the first and second result.
I think the core complaint, though, is that people's first step should be "search using a general search engine" (whether Google or Bing or Baidu or Yandex, etc.) not "search using GitHub". The complaint and expectation is not "someone should have tried to see if it was explicitly on BitBucket", but "people should not assume that you are using a single service". It is effectively similar to "I tried to find your email address and I couldn't" coming down to "I looked on G+ so I could find your Gmail address, and you don't seem to even have an account". There are tons of alternatives to both GitHub and BitBucket, including "I am hosting my repository on my own domain": having everyone assume "well, the content must be accessible within a specific silo" to the point of not even considering "I should use a general purpose web search engine for this use" is an egregious example of "bad monoculture".
