For the hair color its globalization. Just this.. its well knowed in Western countries the love for blonde hair. So
Japan learn more about the western culture -> The western culture will be blend with japanese culture.
If Japan wasn't be opened to the world, maybe Ayu was an enka singer with black hair who wear ALWAYS kimonos. lol
But maybe blonde its just Ayu's favourite dye
For the english titles, I dunno lol.
Maybe they sounds more nice than in japanese.