I found it very amusing reading all these answers which I assume were written by people in the US.
I live in the UK and visit France and Spain very regularly. I believe a resident of any of these countries would be appalled to find a hot/cold shower in a hotel room in Europe - I have not seen such a thing for many years.
All the talk about the the difficulty in manufacturing temperature/flow showers should bear in mind that there may well be 1 billion of them in Europe, and I don't think we can generalise that Europeans are generally wealthier than Americans.
To put in context, I recently had a new shower installed and the shower valve is a ceramic disc, thermostatically controlled mixer with 4 independent flow outlets. The valve cost around £600.link[link][1]. This very much the "Rolls Royce" of shower mixers, but http://www.screwfix.com/p/swirl-vino-thermostatic-mixer-shower-flexible-exposed-chrome-effect/39565 this is a much more basic model for £45 with all the external kit included. I've seen the valve alone for £40 before. [1]: http://www.crosswater.co.uk/product/shower-valve-collections-kai-lever/kai-lever-thermostatic-shower-valve-4000/ "link"
Many people are now installing the next evolution where the temperature and flow are controlled digitally and are adjusted using buttons. Each family member can program their own preference so a single button press will set up the shower to their requirements. I know someone who has had one of these for about ten years.
The point being that these are standard kit in Europe (and Japan by the sound of it) so I think it's safer to ask the question "Why do Americans persist in using hot/cold showers?"