I disagree with you on the walled garden argument - I can read Amazon Kindle books on the Kindle ecosystem series of devices, Apple devices, Android devices, Windows 8 devices, Windows Phone devices, Macs, Windows PCs, Linux PCs, Blackberrys and others.
I can read Apple iBooks on ... Apple devices and Macs.
I can view Amazon Instant Video content on various Kindles, Apple devices, Android devices, Windows 8 devices, all the major consoles, tonnes of TVs natively, and of course Windows PCs and Macs.
I can view Apple iTunes video content on ... Apple devices and Macs.
My content purchased from Amazon certainly seems to be available on a much wider range of devices than content purchased from Apple...