I don't think it's so much the factor of 'audibility" as it is "feelibility."

Most people can't hear too much below 20 HZ. Sub 20 Hz low frequencies can be audible to some people if they are played loud enough. It's more the idea of being able to feel the low bass. Have you ever been in a church with a pipe organ where you could actually feel it playing the petal tones? Thats the sort of feeling alot of people are looking for in their home system.