I follow what you're saying, and that article has a bit of an odd tone.
But I think there is a problem with the way London creates its own self-sustaining myths about culture.
My cousin grew up her whole life in the London suburbs, and I was talking to her and her parents recently, when they all said, totally straight-faced, that she would hate not to be in London because she could go shopping in the evening. They genuinely believed late night shopping was a London-only phenomenon. We broke the news gently but there was quite a bit of disbelief. 
Likewise, when I look at people I went to university with who're in their mid-30s and still living in dodgy house-shares, it's become so normalised. They don't realise we don't all live like that. They talk about how wonderful London is in terms of lifestyle and culture, but they can't afford the culture and the lifestyle is starting to look a bit sad.
I think there's a great buzz, when you're in your 20s, because you're off to the bright lights and it's wonderful, and at that point most of your contemporaries probably are living in shitty house shares and don't have the money to go out. But then, if you never move away from London, you get stuck.
Where I think people actually start moving out is when they start families and suddenly a nice three-bed house in commuter country looks appealing. And I don't think that is really very much about culture, is it?
Not sure what the answer is, but I do think a lot of the appeal of London is hyped up, and relies on people not noticing it's a bit of an illusion.