I see what you're trying to say, but a couple of your statements don't make sense.

"What about editing? Can you go to Dropbox.com, log in, and edit a binary Visio drawing? No, you cannot. With iCloud we get this feature via apps."

To edit a native Visio drawing I simply open the document on a machine that has Visio on it, i.e. a native app. That's identical to your iCloud analogy. But, I can do this anywhere. I can sign into Dropbox, download the drawing, edit it, and simply upload it back to Dropbox where it updates itself across all my machines: my Win 8 tablet, my Win 7 work laptop, my 7-inch Samsung tablet, my Samsung Galaxy Nexus Smartphone, and so on. I don't believe this is possible with iCloud.

"If Apples’ iCloud is a lock in, which I will not argue, how is being tied to Dropbox not lock in?"

It's unclear to me if you really understand the difference here. You're comment leads me to believe you don't, but I know that's not true. I can use Dropbox on any platform. Literally any platform: Linux, Windows, Mac OX, Android, iOS, BlackBerry. And I do. I use it across all my machines and devices. Makes no difference. Correct me if I'm wrong, but I don't believe I can do that with iCloud. That's what makes it a lock-in. And if I choose not to use Dropbox that's ok too. I can simply move to another cloud-based syncing service, or go back to native desktop.