I suspect that the marketing department's idea of what sounds good is often the major factor...
Similar things happen with car model numbers. I read that when Porsche were developing a certain well-known rear-engined, air-cooled sports car, they wanted to call it the 901, only to find the Peugeot had trade-marked all three-digit numbers with a zero in the middle (I guess it only applied to cars!) so they called it the 911 instead.
Allegedly.