I can't confirm that. I used Audacity to generate a series of low frequency test signals, and they go all the way down to 20hz. Even at 30hz the signal is still very loud compared to a 440hz reference signal - that's what I'd call really deep bass extension. I think many people actually confuse extension with gain. Some headphones really exegarate the bass. Listen to a very loud 60hz bass and a more silent 30hz bass and I bet you'll feel that the former is "deeper" - it's the harder for our perception to tell two different frequencies apart, the more we reach into the "extreme" ends of the peceptual spectrum, and the more probable to confuse quantity with quality (or extension).
Edited by timar - 6/2/10 at 5:30am