I think the approach for this should be the same for any site - including a summary of the page, or a snippet that resolves the issue at hand while still linking with "More details here", etc. That way users don't have to click through to get the answer - while still maintaining where the content came from, where to get the most up-to-date information, and where to get additional information from.
I'd like to add to Marco's answer by saying that since the wiki is so big and complicated (and finding things can be difficult) that a good answer summarizes what's in the docs to answer the question and then serves as an "onramp" to the official documentation if the person wants more detail.
On a related note, remember that Ubuntu teams do maintain their wiki presence, so for example the Kernel wiki page will always have up to date info, which is why we want to link and refer.
However some pages on the ubuntu wiki are pretty junk or old. If you run into one of those that are so old that they're worthless to users just delete it from the wiki and put it in your answer as that's what would be best for users.
We need to consider that our answers may now be state of the art but we will have a hard time to keep them update. Linking to Ubuntu resources may help users to find an answer even if solutions and procedures may have changed. This will keep AU a place to look first, even if it only was to find a precious link.
Still, I agrre it is much better to provide and maintain all information in one place. We should think of introducing an Updater badge.