Doesn't "middle-latitude" cover most of the world's population?
> Russia moved its clocks one hour forward to daylight saving time on March 27, 2011. According to the new legislation this is now the country's new standard time. As a result, all of Russia's nine time zones will be permanently two hours ahead of mean solar time, which corresponds to the position of the sun at a given longitude. http://www.timeanddate.com/news/time/russia-dst-law.html