> When did PCs stop being the user's computer / operating on behalf of the user, and instead start operating on behalf of the OS vendor and app developers?

2008-2012

* Apple launches AppStore, immediately starts printing money

* Google launches Chrome, taking web in stranglehold and making it app delivery platform

* Microsoft releases Windows 8, quoting Wikipedia: "changes include increased integration with cloud services and other online platforms (such as social networks and Microsoft's own OneDrive (formerly SkyDrive) and Xbox Live services), the Windows Store service for software distribution, and a new variant known as Windows RT"

* Android starts shift from AOSP to Google Play Services

* Adobe replaced their perpetually licensed Creative Suite with subscription based Creative Cloud

* Spotify and Netflix brought streaming to mainstream

* Chromebooks launch

I think these paint pretty clear picture of the shift we had in computing 15-20 years ago which set the path for reduced user control/ownership of their devices/software/media.

I do think that was very interesting era, and in some ways a peak which almost by definition implies that some downfall followed.