> Why do 90% of Americans have AC while only 20% of Europeans do?

Maybe because the majority of Europe is closer to Canada, latitude-wise, than to Phoenix, AZ, and there is simply less demand? Less wealth is certainly a factor, too, especially considering how the warmest nations in Europe all tend to be weaker economically.

> Why does US have ~4 heat related deaths per million while Europe has ~235 per million?

Maybe its just the higher life expectancy increasing susceptibility? Everyone has to die of something at some point.

> Maybe its just the higher life expectancy increasing susceptibility? Everyone has to die of something at some point.

Ah yes, heat death, essentially "natural causes". Never mind what's obviously in front of your face.