I'm not sure how I can state it any clearer. Desktop Explorer is a superior solution, Metro has little to no solution. A user created file browser has no chance next to Explorer, yet they can't develop one for Metro that needs it. You didn't really address my core point though (RE file oriented vs app).
Look at it from normal users' point of view, not from a developper's. People care about their documents - photos, videos, letters, spreadsheets, whatever.
Most people don't care about the fact these documents are in C:\Users\XXX\Documents - they just want them to be on their computer. Same with contacts - who care they're files? They're contacts and they represent people. The "Modern" interface abstracts the notion of a physical file which is on your hard drive - they're just files stored somewhere. Conveniently, the ones you put in your SkyDrive are accessible everywhere.
You think the desktop explorer is a superior solution because you care about where your files are, and you sometimes want to see files that are not "yours". So do I. But that doesn't make it a superior solution, just a solution adapted for power users.
Yes, that will change people's habits. But that's the point of Windows 8.