State of the Industry
It's true that what one sees in London is in many respects typical of the state of the industry at large.
As for Glenn, in commenting on what was available in London I am aware of how hard it is for an artist to promote himself/herself and keep his/her head above water in such a climate where space is so limited. So Kudos to Glenn for having that many CDs in the London HMV. I wish I lived in a city where you could just go into a store and buy Glenn's latest releases off the shelf.
In Washington, DC where I live, many of the music stores have closed down and the big retailers that remain have reduced their stock and floor space dedicated to CDs (and I have observed a similar trend in NYC). Does this spell the end? To a certain extent, since these trends have a tendency of become self-fufilling prophecies (if there is no where to buy something, no one buys it, then the companies stop making it/marketing it/selling it since they think no one wants it, etc).
But maybe things will turn around. I sure hope so. In a way it depends on what younger people do. I'm about forty myself and don't really have my finger on the pulse or anything, but one hears about a revival of vinyl among some in the under 25 set (especially among college students), but I don't know how significant that demographic is. One also reads that many younger people mostly have MP3 files, don't like to have anything other than the files and often don't even want to pay for them at all. Probably a certain percent still have CDs and don't even have computers, much less MP3 players or smart phones.
As for me, I would hope that CDs, LPs, etc, don't disappear since I too prefer to have the physical object, see the art-work and so forth (not to mention a back-up for filing purposes). Your book analogy is relevant, although there are some disturbing trends in that area of late too, I believe...