Thanks for those informed comments.

So is the main reason they now dominate the form is because they are fairly easy to play and loud?

I tend to think that even one box type instrument tend to anchor the music - perhaps to to its advantage for dance but to the detriment of the music when played without dancing being the main purpose.

Well fashions do move on and I for one hope that this particular fashion does move on - what next Yamaha keyboards complete with built in drum and chord accompaniment?