In an effort to keep this discussion on tone controls. My original Yamaha integrated amp had tone controls AND a loudness knob. Many Japanese based receivers in the 70s and 80s had loudness switches.
This is because the human ear doesn't hear all frequencies "equally" at certain volume levels.
http://en.wikipedia.org/wiki/Equal-loudness_contourTone controls allow the user to adjust the perceived sound to their preferences. Some adjust treble and bass to (poorly) compensate for poor recordings. Others adjust to the sound that they like.
I haven't used tone controls in a very long time, but I understand why some would.
Nowadays, EQs exist in the Virtual realm as well. My music server uses an ASUS sound card and it has its own built EQ as does JRiver Media center. I'm not sure how those work, but I suspect that they're boosting the levels of the signals in specific frequency ranges before the DAC. I run both of those "flat" ie, no boost or cut on any frequency.
I tend to listen to music at medium to high levels of loudness, so tone controls (and the lack there of) aren't much of an issue for me.
HsvHeelFan