I think the points raised are all valid but in my opinion it is all about accessibility...you are correct it is much harder to get on two wheels at the moment, but that is not the only issue.
You can buy a car (one that will impress the girls, or boys for that matter) for near on nil deposit, pay £99 per month and hand it back after three years. Why would you even bother with a bike? Which in turn means you don't get bitten by the bug.

There is a lot that can be done to correct this, and I do not think that two wheels is necessarily a finished proposition. Governments will see that they can play a huge part in a low carbon, low congestion traffic solution.
Also wait until at 17 all you can buy is a four wheeled electric egg whisk, you might start looking around for something more exciting.

As for the original question, I think in general there are less and less of these bikes available and people are getting much more affluent (all around the world). I can see the Japanese buying them back from us one day soon!

Les: I think you better pass that 125 over for some TLC, I will happily make a racket on it at any track that would have me!