That has been a big topic of discussion. It seems that a shared appendix of information would make an easier job of editing and updating. Although copy and paste info into each platform site is almost as fast, and gives the benefit of not linking people into limbo space – where they loose track of what site they are on. This can cause stress for some folks.
The easy way to do edits of common pages is simply to edit one copy then do a global select copy and then simply over write each of the other pages with a global select and replace command.
We probably should pick one of the Wikis as the root Wiki for common pages though because media will be easier to deal with when stored in a single Wiki. (The media address will stay the same).
Less than a minute per copy.
This really is the best way because the user stays in the same Wiki so navigation is contiguous.
Unless WordPress has some way around this, separate pages are a better way to go.