So, even though those two frequencies are inaudible, the beats will be audible. Without both frequencies, however, the beats are lost. Pipe organs use this principle to get some of that great, big sound. A psychoacoustic encoding algortihm might well lose one of those essential inaudible high frequencies. I don't know.
People can argue it left and right.
So, to sum up. Both MP3 and Minidisc remove information from within the frequency spectrum of a recording. Theoretically, they have unlimited frequency range, whereas tape, for example, will simply lose very high and very low frequencies. Of course, these algorithms are likely to filter out those same very high and very low frequencies, but, theoretically, only if they are inaudible. Most would agree that it does.