The Dropbox app creates a local copy of your data that will sync with your data in the cloud. The result of this is that you always have a local copy of your data. If you stop using Dropbox all the data remains where it is on your computer.
Ok, you do have (kinda) a point with Dropbox since they store the file locally on all computers.
What I'm saying though, is that the cloud storage (not local) can be decoupled from the service. Such that if I decide I don't want to use Dropbox anymore, I still have a access copy of my files in the cloud - just not via the Dropbox software.
Imagine if Dropbox sync'ed your local files with your personal Amazon S3 bucket. That's what I'm hinting at.
The Dropbox app creates a local copy of your data that will sync with your data in the cloud. The result of this is that you always have a local copy of your data. If you stop using Dropbox all the data remains where it is on your computer.