If only it was that simple. All amplifiers roll off high frequencies, why you might ask. Well simply put, if the frequency becomes high enough you get pure DC output. The amplifier also feeds the speakers which have their own built in high frequency limits (my speakers have two super tweeters for sound dispersal).
If you take an audio frequency generator and wind it up to above the threshold of human hearing then the amplifier would roll that frequency off as there is little point in creating an amplifier that delivers that frequency as it can only be heard by animals. Designing an amplifier for human hearing is far more practical and easier to achieve.
Naim amplifiers are known for rolling of the high frequencies, it was probably accidental, but the result of doing that is that the mid to low frequencies become more obvious. Hence the rhythm of the music is far more audible.
Now, if you know anything about music as opposed to simply generating perfect sound, then you will know that for all intents and purposes rhythm is the music, without it sound is just meaningless noise (although you can always invent a pattern of sorts from the chaos).
Does this make some kind of sense ?
As long as the cut off of frequencies does not interfere with overall sound of the music then it's importance becomes minor.