This is an excellent article so I thought to share it with you all. Here's a sample....
"Differences among speakers exist over their entire range: Lows, mids, and highs. So, over the years, mastering engineers have recognized that the only want to deal with this madness is to create a recording with the flattest, most "average" response possible. That way, it will sound only a little bit "wrong" over every system, rather than okay on some systems and way wrong on others. (The exception is that of the audiophile with the really flat system - who after putting the requisite time, expense, and effort into assembling a great system, should be entitled to the best possible sound.)
It's difficult to create a truly average midrange response, because that's just one of the places where speakers exhibit significant differences. (An aside: I always get a kick out of speaker reviewers who breathlessly exclaim that a particular speaker "revealed things I'd never heard before in my favorite recordings!" This isn't surprising, because any speaker will reveal things you've never heard before, as it's basically EQing the recording differently.)
High frequencies are a different matter. The energy in real music tends to drop off fairly rapidly above 5kHz, so really, what we want is a "sensation" of brightness. You're not going to get the huge peaks caused by notes piling on one another, because there just isn't that much energy up there. A little bit of a boost in the "air" range above 10kHz will do wonders for making a mix transportable, as the tweeters open up a bit more. As a bonus, most playback systems have a treble control that can be trimmed or boosted according to the listener's preferences, based on their acoustics and how shot their hearing is from going to too many concerts without hearing protection."
more... http://www.musiciansfriend.com/document?doc_id=104319&src=3NL8KU&ZYXSEM=0&Prime=Bass
