I believe it'd be quite difficult to implement a mechanism to separate posts from edits on a per-namespace basis. Also, core MediaWiki would probably not allow for this to be merged back, which means that Wikia would have to keep the code up-to-date all by itself.
Which shows that there's already a count maintained per namespace, meaning it would be trivial to allow the database call for that value to be a customisable so that the editcount in the user header can display something other than "all edits".
For instance, showing only edits in the content namespaces of a wiki would be desirable.
edit: although, I hate the editcount being displayed to begin with, as the quality of edits are more important than the quantity. The fact that I often have to go back to fix a typo I made, or add something which I should have thought of early should notbe "rewarded" by having a larger number displayed so prominently in my user header.