That is true, and to the extent that those cloud applications don't use an open interchange standard you won't be able to share documents with them. Having lived through this from before[1], it isn't as dire as you might imagine. What happened last time is that it forced a lot of interchange formats. Will be interesting to see if it does that again. All of the market forces are still there, person A wants to send a document to person B, etc. Of course everyone can send HTML or RTF documents like they do today.

[1] Intel used MultiMate for its documents (as did a bunch of lawyers) while nearly everybody in the tech space was using Interleaf. Xerox was trying to be the paperless glue for the middle. We got PostScript out of it, which was an interesting compromise.