I've always kept my Quicken data on an encrypted/mounted volume. Understanding that if that software layer ever hiccuped or went bad, that data was at risk - hence backups. Knowing full well though that it's more reliable than any cloud service simply because there's less "stuff" for my data to travel through on its journey to the storage medium. Though I presume those providers services have measures in place to retain data integrity in the event the connection gets bumpy.
I wonder if Quicken has changed things under the hood regarding disk I/O or if they are just doing this as a precaution because they end up seeing allot of problems with data files stored in cloud services?