This isn't about iCloud vs. Dropbox, this is about giving users choice. You can ONLY get apps through the appstore, and they won't post an app if it does A, B, or C - including sign up for dropbox/google drive?
This is in no way good for the consumer.
And I sync up files from various devices that cannot be done without using Dropbox. iCloud is nice but it doesn't allow me to sync a Mac, Windows PC and my Android phone.