I guess I see the point behind this mentality, but at the same time I don't really agree with it.If you're adding content, please focus on documenting things which aren't already well documented; if it's already documented, just provide a link. A goal of this site is a coherent organization of information already available
To me, the wiki seems like it should be a living, all-in-one massive reference. Rather than just a compilation of various links to offsite pages. I mean... if someone just wants a compilation of links to various docs... they'd go to the main nesdev page.
Not to mention you can't make minor corrections/clarifications to pages if the wiki is just linking to some other doc. So that takes away all the flexibility and control of having a wiki.
I don't see the harm in copy/pasting chunks of info from existing docs. If credit is an issue we could tack on a "contributors" or "sources" section at the bottom. In fact the sources section could even link those off-site pages... in addition to having it available for viewing/modification on the wiki.
Imagine doing a search on wikipedia... only to receive links to brittanica and other encyclopedia sites. Makes you kind of wonder what the point is =P