If bi-amping is so great, why do some high end speakers not support it?

@kalali 
The benefit of doing that is the speaker cables are kept shortest, while one channel will be a lot more demanded that the other one just because of power draw for each band.

Alternatively, using the same two stereo amps, one for L and R bass and the other for the top will give a balanced draw for both channels at each amp at the expense of longer speaker cables.

Level matching amps from the same manufacturer.... No that is completely contrary to what I am trying to achieve. I want to have control of the treble and bass separate from each other. I don’t always agree with mastering engineer decisions on how the record should sound. In those cases where I feel treble is out of control or bass is severely lacking , I want to be able to use tone control and volume separately for Treble and Bass. So when particular recording or my own speakers don’t deliver desired tonal balance to my ear I will intervene and adjust to my liking.
On a side note; I have heard that tone controls are frown upon by purists, but to my logic : why spend thousands upon thousands on your gear and listen to someone else idea of the music instead of adjusting it every time to your particular liking?

dkzzzz, tone controls are one of those things that purists as you say, don't like.  I agree with you and I know many designers who also do.  That said, I've never heard digital EQ that didn't somehow change the sound of the spectrum elsewhere in the speaker.  Many of you will disagree and that's fine, but I've heard a lot of digital EQ done with very high end system and or speakers that have it built in and I haven't felt the results were worth it as you help alleviate one problem, while cause another one.

I've heard a system using a parametric EQ that, to my ears, did a really good job, but you really have to know what you are doing when using one.  Many of us love 70/80 rock and could really use a pre that offered it in somehow.  Most of the recordings are really hot on top and they mess with the rest of the spectrum also.  I have been in a few studios back in the day and saw engineers making tiny adjustments, but it was always riding a gain pot and it almost seemed that they wanted to justify their jobs and validate what they do, lol.  Not taking shot's at the engineers, but we hear what we hear on the recordings and most will agree that they aren't usually the best sounding.  Great music though and that's what it's about.

Sorry I caused some confusion by writing bi-wire where I meant (vertical) bi-amping. I asked a more specific question in a Vandersteen thread I had already started.

my comments are limited to biwiring of which there is science ar work the case can be made that a bass cable in close proximity to midrange cable WILL modulate the HF signal by changing magnetic field.
hence Vandersteen staking out a strong scientific and listening based preference for external biwiring...
download one of his manuals for a nuanced approah to getting more out of your system ( speaker placement in the room using,,,,eek math !!!) as well and bi-amp, vertical bi-amp, biwire, etc