Dropbox is a lot different, though, when you think about it's core concept. Dropbox doesn't do anything that necessarily is novel. Dropbox allows your computer to function as it should--documents should be backed up, safe, and widely accessible. Dropbox merely supplants the role of redundant hard-drive backups and e-mail file transfer. But we've lived with e-mail and file systems for long before the creation of Dropbox. Dropbox is easy to understand because it hasn't added something new, it just helped us live our digital lives with convenience.
iCloud shouldn't be easy to understand because it's introducing an entirely novel concept to our digital lives, which is to lift the burden of wires and a fixed connection off consumers. This is a genuine step forward in the movement to unleash our digital lives. It's a totally novel concept so it should be difficult to understand than services like Dropbox.