Long term (as in a few versions out) if wiki becomes much more heavily used there is stuff we could do without needing to resort to locks.
Off the cuff, my initial reaction to “fixing this” would be to add a red highlight around an area that is being edited at the moment by someone else (only in the editor) it would allow you to easily avoid duplicate editing, further more we could apply “diffs” when saving edits to avoid an edit killing an intermediate edit.
Always been facinated by http://sharejs.org/ and stuff like that
I do feel its quite low priority though for now, at least until wiki gets a very big workout somewhere.