I agree with this.
Even lowly earbuds that have very little bass and sound like a stampede of hungry cows can sound good with proper seal. That is why there are aftermarket products for iBuds and their ilk. High end earphones sound much better of course, but really really good with a nice seal.
The other thing is housing quality, particularly when hand in hand with loads of bass response. The first being bad, the second will boom and echo till only slow hip hop is listenable.
As a designated member of the trade, I can't slag any competitors on this forum. However, I do have a few quick observations:
1. I am more and more convinced that the biggest barrier to quality IEM audio is user error, specifically failing to get a full seal. I strongly suspect that it is this, moreso than personal taste, that accounts for the huge disparity in perceived bass response in the same model. (In all fairness, there are plenty of universals out there that make this task more formidable than it should be.)
2. There is plenty of bass, and significantly extended high end, in BA drivers. For those who don't agree, see #1.
3. I rate this thread extremely interesting.