Don't know about iTunes, but much along these lines Sonos removed support for Windows DRM and ticked off customers who had their music stored in that format. Amusingly, the link I found about it is also a post by Cory Doctorow.

https://boingboing.net/2011/12/22/sonos-removes-windows-drm-...

I suspect the Kindle feature he's talking about is the text-to-speech feature, which the publishers hated because it threatened audiobook sales. Or maybe he's talking about Amazon deleting books from customers' Kindles?

https://arstechnica.com/gadgets/2009/07/amazon-sold-pirated-...