Regarding stackoverflow there is a fair chance they can congratulate themselves:

If I am right they played stupid games and won stupid prizes. More specifically they have allowed rampant deletionism for years so while I am fairly certain the questions and answers originated on Stack Overflow it wouldn't surprise me if a good number of of those aren't visible on Stack Overflow anymore which would explain why they rank higher in Google.

Done right this would actually be a service.

Sadly some of them seems to mix together various questions and answers in the same page to generate text matches for unusual queries.