Rectifier Tubes

Hi all, can anyone tell me why I hear so much of a change in my amplifier's sound (Coincident Frankensteins; 6em7 driver tube, 300b output tube) when I change the rectifier tube? 

I just got the following message from a tube vendor:

"Further, rectifier tubes (5U4) don't pass or amplify any sort of signal so our policy of no returns for tone especially applies to rectifiers. Changing a rectifier tube shouldn't change the tone of your amplifier at all, not even a little bit. This is why many high end amplifiers have solid state rectifiers. "

They actually did authorize a return (I was returning because the tubes were distorting, not because of tone), so I'm not gathering ammo for a fight.  I'd just like to understand why my experience is so different from this (presumably highly knowledgeable) individual's beliefs.

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The gain stages of any component, will utilize devices(transistors, MOS-FETs, valves, etc) that modulate, as directed by their input’s signal, the voltage/current, from your power supply, to the next stage of amplification, or- the component’s outputs. Basically, you’re listening to your power supply. Upgrading a power supply’s rectifier(s)* and/or regulator(s) whether SS or valve, as well as capacitors, will(generally) be easily heard(ie: cleaner, smoother, more dynamic, etc), whenever done in a high resolution system. Some manufacturers that offer upgrades to their gear, focus on the power supply, as the primary target to address. *ie: with soft/fast recovery HexFREDs, HiPerFREDs, Mullard Blackburn factory, or big, funky, Phillips valves
As I said on another thread, rectifier tubes drop different amounts of B+ voltage. This will affect operating points in an amplifier circuit. It is best to use the original rectifier that the circuit was designed with. Otherwise you are second-guessing the amp designer's goal in achieving a certain sonic goal!
And rectifier tubes each have a definite limit on their current-handling! A 5AR4/GZ34 can handle considerably more current than a 5Y3 (typically used in preamps). An over-stressed rectifier will start to glow red and will eventually fail! 
At the top of rectified full wave sinewave current changes direction but rectifier is too slow to respond and keeps conducting in opposite direction for a moment then snaps back to zero current. Fast snapping back creates very narrow negative current spike, that can couple to any inductance in the circuit, inducing electrical noise (narrow pulse contains all frequencies).  Better "softer" rectifiers like Hexfred snap slower to zero producing wider (less dangerous) negative pulse.    I suspect some of this might apply to tubes as well.
In some tube pre-amps I've owned the rectifier was THE most important
tube for sound .
Ideally, a tube characteristics is less important than the filter that follows it.

The tube rectifier will determine the voltage, but ideally, the filter should eliminate noise, and is responsible for any supply sag, not the rectifier overall.
I guess this is quite variable.
Thanks for the information everyone.
I have a deep respect for those who have electrical engineering backgrounds.  They bring so much to this forum!   I do not have a background in electrical engineering, so I tend to make judgments based on empirical evaluation rather than first principle considerations.  But based on my simplistic empiricism,  I am amazed that anyone with normal hearing, especially a tube vendor, would dispute that different rectifiers, and here I mean different brands of the same type rectifier as well as different types of rectifiers, can have a profound effect on how a component sounds.  For all I know all of this may be limited to differences in sag or rise times.   I'd love it if all rectifier differences could be attributed to measurables.  I will say that I have noticed some pieces are more influenced by tube rolling than others.  Perhaps Erik's comment is relevant to that phenomenon.   
Of course we all respect EE grads, one of hardest majors in any university .But , just because it was so hard they sometimes cling to things that have been proven wrong by neurology which has made huge bounds and leaps
in last decade .Perhaps the greatest of any science  in that length of time in history .