IGH, Alfine, Rohloff, Sturmey Archer and frames/bikes built for them...

Questions that come to mind are why aren't there more out there?

Charge used to do em - the Mixer for example. I had one, now my cousin does. It lives out its days in Singapore :)

The market is small in the UK I suspect because

1. The ones that work are not cheap (Alfine, Rohloff) and the people who would benefit from them are largely buying on price
   
2. Those that understand their benefits also understand how to keep a derailleur based bike going
   
3. The cheap ones don't work - they fail, and completely, unlike cheap indexed gear systems which can / will stagger on
   
4. Shops can't service them, or won't, or won't after losing money doing something notionally simple like puncture repair