I think Google prefers to programmatically detect and blacklist behaviours, without too many innocent casualties - even if working out how to do that takes longer. They aren't interested in playing whack-a-mole.
Although this is perfectly legal, there is quite a few big sites that scrapes Wikipedia and adds ad-sense. If you are searching for a narrow topic, page 1-2 is WP and WP copies.
As a sidenote - I see that Google Search has upvotes, comments and deletes in the search - yet it does not seem as if anyone uses it. Why? Why can't the user at least blacklist sites?
It would be good to have a "remove all pages with Wikipedia content" button on searches. Sometimes it seems half the results are simply Wikipedia copies.
And at the higher level they absolutely do penalize people individually to send a message. Watch the opening of this video if you think otherwise http://blogoscoped.com/archive/2008-07-08-n14.html