Agree on the sentiment but not the facts
Much as I agree with the sentiment here -- I have always viewed Robertson as someone who is obsessed with goading the music industry through copyright law boundary tests disguised as startup companies (see http://copyrightandtechnology.com/2011/08/23/mixed-verdict-for-emi-against-mp3tunes-com/) -- I have to say that unfortunately you're not correct on the facts regarding Google and Amazon.
The truth is that while both of them have licenses from the record companies to sell MP3s, neither have licenses tat support locker services, i.e. users syncing their files among multiple devices. (Apple does, which is one reason why they do "scan and match" in iTunes Match, the feature that lets users sync their music files without having to upload them.) This is Robertson's central innovation; he was the first to market with sync via downloading -- as opposed to upload-and-stream which is what the likes of MyPlay offered earlier.
The record companies have chosen not to go after Amazon or Google for download sync... so far.