Sadly, anyone who claims not to hear a difference between any compressed codec and uncompressed PCM is either not using a very good system or not using their hearing properly.
The differences between AAC/MP3 at 128Kbps and even the lowly 44,1Khz 16-bit CD is very obvious, as long as you know what to listen for. This is nothing to do with "audiophile" snobbery, it's just the professional discernment of people who use their ears for a living.
I'm not suggesting that AAC is bad, it's a marvelous codec for producing very small versions of tracks for iPods, and it's much better than MP3, but it is an inferior quality version to the original.
On a well maintained professional monitoring system I can hear the differences between 44.1Khz, 96Khz and 192Khz, and if available 1/2" or 2" analog tape as well, I can hear differences between DA converters (Apogee are slightly more musical) and I can often tell you which mic was used to record a sound...😀
This means dick in a real world situation, and is only of interest to professional engineers who work at the extremes of recorded sound. My iPod is loaded with 320Kpbs AAC tracks and it sounds OK on the train to work, but I wouldn't dream of putting it through my stereo at home, it sounds poor.
Loaded with Lossless files or .aiff uncompressed files it sounds pretty good, but still not as good as CD.
I'm certain the bottom line is that most people are perfectly happy with 128Kbps files, and thats exactly what they get.