1) You usually listen in your car, and road-noise alone will destroy your ability to discern slight volume changes and perception of frequencies anywhere near 12khz and above
Actually, I usually have talk radio on in the car...
2) If you don't listen in a car, you often use your cheap speakers on your laptop
Can't say I do that either. Sure, sometimes I'll use the lower fidelity of headphones/earbuds hooked up to my iPhone, but that's not where most of my listening takes place...
3) Most headphones people use are either cheap (under $50), or they are biased on the lower-end, and most are not equalized correctly, or not equalized to your ear physiology (different sizes ear canals can cause resonance/standing waves that cause a different perception in frequency for different people -- each set must be tuned individually if you are a true audiophile).
Well, the headphone/earbuds I usually use fall in the ~$70-100 range, even though I'm not an "audiophile" since I refuse to pay $400 for magic ethernet cables...
4) If you're older than 21, you probably can't hear above 16Khz at all
Well, my ears aren't as good as they were ten years ago, but I've tried to avoid the normal things that cause hearing loss and damage (such as, I dunno, obscenely loud music?)
5) Your ears are not perfect (many people's frequency response is different from one ear to the other)
6) Your player is not perfect
7) Your speakers are not perfect, and you most likely haven't calibrated them with an RTA for the room they sit in or for where people are actually positioned.
8) The humidity, temperature, air pressure, and even the air pressure on the other side of your ear-drum changes frequently causing a difference in frequency response.
And if I'm completely wrong on points 1-8, then you are now in the .01% of all listeners, and you are not the target audience for mass-produced and distributed MP3s anyway.
Though I never said I was the target audience for "mass produced mp3's", your post really comes across as a snotty "audiophile"... I've pretty much stopped listening to the Mp3 format. The music on my iPhone is mostly 256kbit AAC with a sprinkling of Apple Lossless. One of the reasons I often buy CD's over downloaded is because I know I have them in the most lossless and unencrypted format available to me. There are a few high-end sites (such as Linn Records UK) that sell lossless FLAC format music not only in standard CD 16bit/44.1khz but also in higher resolution "Studio" quality formats 24bit/88.2/96khz, some tracks are even available in 192khz. The "modern" pop/rock/etc. stuff isn't as much of a big deal but when dealing with stuff that is a lot more about the acoustics then you better believe the audio fidelity makes a difference.
Of course music that is produced with the intent of distribution at the higher resolutions often has higher production values anyway since they are targeting a different audience that cares about such things as the dynamic range and who are more likely to pick up on subtle issues whereas many "joe listeners" prefer the sound of the lossy compressions since that's what they have been raised listening to... sad really.
Sure, I don't have $10k speakers or a $20k receiver, but I can hear subtle differences, even if some of it may be attributable to placebo effect. I do have equipment that can handle some of the higher resolutions both on my primary stereo system as well as my primary desktop system. It find is much easier to down-sample a 24-bit/88.2khz track for whatever my listening environment may be then to do the inverse for when I wish to really "enjoy" and "experience" the music.