As the frequency goes up, so too goes the price tag for amplification. Folks aren't as concerned with the quality of bass amplification as they are with the midrange region but both pale in importance to the attention and money paid to get the tweeter's range perfect.
Think of all the ways we've worked on to sweeten the top end: tubes, low feedback, single-ended outputs, high class A bias.
When it comes to bass, we just want it to go deep and powerful.
Fact is, the higher the frequency the greater the engineer's challenge to maintain purity, phase accuracy, and transient speed. Harder still is designing an amplifier good enough to handle both the power and depth of low frequencies with the delicacy and transient speed of the upper notes of music.
It is the rare piece of amplification equipment that gets high marks for all frequencies, but it is the upper ranges that we fight hardest for.
We can forgive "ok" bass but screechy highs are unforgivable.
