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

Multiamping needs active filters to start making sense (today mostly with DSP). Speaker passive crossovers should be removed. Whether such configuration can sound better is a matter of implementation. With very good amplifiers and passive crossovers speakers can sound excellent. IMHO digital filters need to be done with at least 172 kHz sampling

Theoretically, biamping can be better due to bypassing crossovers. I have found that my pair of Audire Forte amps are less fatiguing when biamping my 803's, but my slightless less powerful class A Audire amp does not need to be paired to maintain the best sound. Of course, subs are required either way, and the Forte's excell with them.

For you who are not aware, biwiring does not exist electrically. Use a 20 amp capacity wire vs. 2 tens. There is no difference. You might say use 2 20's? Then use one 40.

Folks can say what they want about bi wiring, but Vandersteen designs all his speakers to be bi wired and they do sound better doing it.  I trust my ears. I know what engineers may say, but again, the ears don't lie.  There are plenty of things that can't always be explained in audio and that could be because we don't have the measurements for them yet.  

Since Richard has no skin in the wire business, there is no way he'd espouse this if it didn't make a difference for the positive in his speakers.  

I've also heard them bi amp'd.  Once in a store, I didn't like it. He used less than stellar amps doing this.  Another time when I heard at a friends house, it sounded the best I've heard the Treo's sound. He was using all Audio Research amps and I think keeping in the same company made the world of difference.   JMHO

For for those engineers who dispute what I am hearing, the fact is that you can't because you aren't in my head, lol.  All of audio is subjective.  The first time I heard bi wiring of the Vandersteen's, I had no idea that he was changing anything in the system.  I was listening to a track and then he took a few minutes and unhooked the second run, but I didn't know it.  It was pretty easy to tell which was which.  I know many who feel the same way and some, who have never heard the Vandy's both ways, make statements about how they sound....even though they have never heard them.  Just saying.