Whilst I don't got up to the smaaaaaaaaaaaahhhhhhhhhhk (as we Londoners say [ha ha]) very often, a quick browse of the Time Out Restaurant Guide (*) suggests that funky, marginal cafes are probably not dead. A Google search for London unusual bookshops looks similarly promising. Galleries I cannot comment on, really, but I imagine that he is just as full of shit there.
Then again he may have more exacting standards than I. My tastes in food are mercifully cheap, and if anything getting cheaper, and the places I like may not be funky and marginal enough for him.
Nor do I think that what he says is any truer of New York than London (I think that New York may suffer by comparison to London due to having a clearer geographical distinction between Manhattan, the other boroughs and places that aren't in NY city, or state at all, whereas London bleeds out more slowly until, bugger me, you find yourself in York or Brighton or on the Eurostar to Paris). On the whole, I do not buy the 'people leave the big cities to go and do exciting things somewhere cheaper' theory.
(*) I subscribed to the on-line version once due to the hatefulness of anything free when I was trying to find somewhere to go for a birthday or something, and when they stopped charging for it they refunded the remainder of the subscription which I thought was beyond the call of duty, so fair dos to Tony Elliot (if he still owns it)