I'm much more convinced Microsoft wants to do stuff like sell cloud subscriptions at the click of a button in the desktop than Microsoft gives a crap about those subscriptions being tied to a consistent account ID. The latter certainly sounds evil, but not in a way that particularly helps Microsoft over their competitors.

Uncle Bob probably would probably need to do a decent amount of work to figure out how to purchase a OneDrive subscription from having no account, particularly if they think "I've already got an account - that's how I log in!". If the PC forces Bob to walk through creating a cloud Microsoft account before he even sees the desktop then the only step remaining is to click to OneDrive (or whatever) sales notification and enter a credit card so his "important personal files stay backed up" (or however they pitch the service in the notifications).