That is an excellent point. I recently switched from Google Docs to Org files with Unison and ediff for syncing. Having everything work offline and on, over multiple machines, and being able to review and merge changes really makes things much more convenient. I now have multiple local and remote backups and no longer have to worry about losing my Google account. Another common pattern is to diff files that come in over email, or to diff when someone takes my code changes and modifies them by hand/rebases them.

At this point I think that plain text files in a distributed version control system that can also import/export patches for emailing (like darcs and git) is clearly superior to cloud-based document storage. The promises of the latter have just not panned out - what we got instead is vendor lock-in and the Damocles sword of account lock-out/deletion/hacking. In many ways (UI responsiveness, control of data and privacy, service discontinuation due to vendor shutting down product/acquisition/bankruptcy, etc), the cloud apps are a big step backward from PC applications.