The strangest thing just happened to me while I was typing in MS Word. I wanted to stress something and used *'s to do so.. Suddenly, it turned bold. I've used Wiki style formatting before but I didn't suspect that MS Word also had these kind of shortcuts. Similar thing happened when I used underscores.. The text style changed to italic.
People have been using those marks to indicate "virtual formatting" in plain text since long before the term wiki showed up. So it doesn't surprise me that at some point MSWord developers thought it'd be a good idea to autoconvert it.
BTW, the only wiki software I've ever used doesn't even use those marks for formatting.
