It doesn't matter if it's a proprietary format. Proprietary formats can be reverse engineered and modified and converted. There is a world of difference between a proprietary file that I have online in a form that I can't access directly (and I have no idea how it's being accessed, changed or stored by the service itself or third parties) and a file that I have on my harddrive that I have complete control over.

Yes, but I think most people care about availability of data over true ownership of data.

If I’m running a business and my internet goes out, there’s a huge selling point to a local DB that allows my operations to keep chugging along until Comcast figures out their mess. Internet returns, my DB syncs with a server offsite, and now I have that backup.