Yep, there isn't as much high frequency content in sound in general. Think of how bright/blinding sounding the world would be if there was! It would sound just like... some of those volume war mastered CDs that also have the treble cranked up to 12 (which is higher than 11)!
This leads to "Why is my mix muddy?!" The lows and low mids stack up when you add together recordings of multiple elements. The trick is to keep just the right amount of girth from appropriate elements. Go too far and things get tinny and you're into shit-mastered CD territory again.