Earlier quoted context omitted.
Canonical provided an answer here: http://askubuntu.com/a/15295 . I think the answer is interesting, and this could apply equally well to any other vendor.
That's a silly answer. The technology behind the syncing is not a competitive advantage. The existence of dozens of these services should tell you that. The way the companies can compete is by building services on top of the cloud syncing, and by providing integrations with other services you use. That stuff makes sense to be proprietary, but the syncing itself doesn't, imo.
I'm not sure your argument applied at the time. As technology makes progress, today's competitive advantage is tomorrow's commodity.
In any case, consider the people who pay for Dropbox today. What proportion of these people don't use integrations or services on top of the basic sync service?