I don't quite like the title because it implies HP is trying to silence the author or something, but if you read the email it just says they're adhering to a content policy they have. Which the original author should be aware of, since he's writing for them.
In any case, the whole spotify thing is a house of cards waiting to fail. They have brand-name recognition, but like the author points out (really well!) they don't have anything that keeps you from switching. I pay them to play music. I can easily do that through another service, as long as the music is there. In fact, if I were made aware of a better alternative I would..... will be spending some time later looking some things up....
But I think therein lies the issue with the whole streaming model. Can you really have an alternative? You can do something like apple does, with (temporarily) exclusive music, but that tends to piss people off. You can try to renegotiate the deals made with the labels, but aren't the labels just as much at fault as spotify??? Why is there always yelling at spotify but not at the labels for making these deals? I mean they're standard, on the webs -- google play/apple app store also take ~30% off the top.
So to make a more 'fair' streaming service you'd need to get content (become your own label? tricky, hard, outside of the scope of the project) or negotiate better deals (which if labels cared they could do with spotify, but they don't?), or introduce a price hike to compensate more fairly (there's a reason pretty much all music streaming services are at ~$10, because no one can afford a higher price than others right now). Add on to that that the big labels pay money to spotify to get their artists promoted (those 'just for you' playlists are more like 'just for the label' with handpicked content that's slightly adjusted based on your taste, you won't find smaller/indy/non-promoted artists there).
What I'm saying here is that I htink it's a bit unfair to blame it 100% on spotify. Yes, they're dumb and unaware, but the labels are to blame too, as are consumers, the system, etc. I don't think there's quite an easy fix.