Hard though it may be for people that live in the Valley and work as programmers to believe, most of the world isn't permanently connected to adequate-speed internet. For the 99%, they do need to worry about where files are stored, specifically why they can't access them even on the laptop they used to create them.

That's why Dropbox will continue to annihilate any service that doesn't locally save data. If my files are in Dropbox I can freely access them on the laptop I used to create them whether I'm sitting in a hotel that has so many stars you have to pay for WiFi or on a beach in Thailand. And the next time I have my laptop on within the range of publicly accessible free WiFi, it's all in the "cloud". If the internet connection is extremely intermittent I can have my updates save asynchronously without the endless frustration of browser error messages (or even worse, an Ajax smokescreen concealing the failure of an app to update server-side).

And even if I'm sitting in my office with a perfect high-speed connection doing average office work, the chances are that at some stage I'll be using a program with functionality not available in filesystem-less SaaS. In which case I don't really begrudge the extra few gigs of disk space Dropbox takes over pure cloud hosting.