If you take a look at Wikipedia's page on Equalization, it shows a picture with the high and low tones boosted, while the mid tones aren't typically touched. In addition, I know I've seen this on multiple other equalizers that I've managed to catch glimpses of -- It could just be that I see that pattern and register it more often because it's an easy pattern, but it seems to be a de facto setting for equalization. I've reproduced that with my equalizer on my headphone software, and while I can tell a difference in my music, I wouldn't necessarily call it better or worse. Is there some reason for this (de facto) standard?
This setting tends to fit with the Fletcher-Munson curves.
Basically, it says that human hear is more sensitive to mid-frequencies than it is to low and high frequencies.
At low volume, we don't hear low and high frequencies as well as we hear middle frequencies. At high volume, we hear them all quite equally.
This equalization setting (sometimes called Loudness compensation) tends to compensate hour hearing weaknesses by increasing those frequencies so in our perception it will sound like high volume (i.e. we can hear all frequences well) without the volume being actually very high.
You can try this experiment: Pick a song you like much and play it at a reasonably high volume (don't damage your hears!), then lower the volume and compare with applying this compensation and without.