[zzalpha]

That's not strictly true. Network effects due to tied services can result in barriers to switching. For example, if you're tightly tied to iCloud, migrating to Google Drive might be seen as an enormous PITA.

IMO, this is the principle reason all of these guys are building easy-to-use, tied services offerings... because the OS is becoming increasingly irrelevant as things move to the web or apps go cross-platform.