Why would anyone make Joe Average use Textile anyway when there are plenty of rich text editors available? Many (most?) have button bars Joe would be familiar with if he's ever used MS Word (which most Joes have). And again, many are cheap, free, and/or Open Source.
A properly configured app that filters user input doesn't need to require users to know any markup languages at all. So why?
Stop thinking like geeks and think like users.