For those interested in what's dropping in the fall with iOS7, it seems that there will be a slight change in the way Wikipedia search is integrated in to Siri.

Currently, you would need to explicitly use the name to search Wikipedia results alone or primarily ("Search Wikipedia for surfing" or "Wikipedia surfing"). It seems that they'll be using more natural language in iOS7, with phrases such as ("Tell me about surfing"), and also using something a lot more like the information snippets in Google Now or Quick View.

I'm fiddling with it on the iOS 7 beta build. Saying "what is X" seems to reliably pull up Wikipedia articles, as do some similar natural language queries. (But if you ask about anything Apple-related, Siri just tells you you should go to apple.com. What don't they trust us? ;)

Here's a screenshot from today's keynote, which to me seems thin on attribution...

Here's a combination shot showing what you get when you scroll down on that 'surfing' search:
https://brionv.com/misc/siri-ios7-surfing-wikipedia.jpg

Somewhere down at the bottom it does actually say "Wikipedia", and if you tap on that it takes you to the Wikipedia article in Safari. Not the most visible attribution, but it's sorta there. :) It also shows a lot of related queries, which come up in the Siri view as well when tapped.

-- brion