The thing is, there aren't actually that many file types which you'd want to open in multiple programs. Maybe fifteen or so which you'd expect to do data interchange with - a handful of picture formats, ditto movies, ditto audio, ditto text/DTP, and Excel and Powerpoint.

Everything else is special-purpose, so as long as you can mail the document, you're fine.

iTunes and iPhoto already handle the majority of those. Add a personal office-document-management tool and you're already pretty much there.