They are trying to solve more than one problem but end up creating an unappealing solution. The real issue here is data portability - not data migration. Moving my e-life to a web based desktop will never work. Some of my documents are too sensitive to store online. What if I am using a browser with limited functionality. I'm a student and in a given day I must be using more than 3 different computers at least - all of which have a different system with different access restrictions. I wish flash worked properly or even existed in some cases but that is not the reality for people who really need this.
These products are all built on a notion of "what if we could..." not what is actually needed.
At the end of the day I want to access all my data anyway I want - usb, internet, ftp, http, pop, imap, ssh, sftp, yada yada. Now that would make my life so much simpler.