If there are so many variables then why even bring up the old argument that
all amps sound the same?

Because it dispels the many myths out there that revolve around the notion
that amplifiers have a "sonic signature". It points out that comments
attributing one type of sound to amplifiers made by one company, and
another type of sound to another company, have no basis in fact.

The fact is that in real world situations you
usually get what you pay for. Given that at some price point the benefits
are not significant to justify the extra dollars.

This is exactly true, within limits. While it's true that oftentimes
spending more on an amplifier will get you better reliability, better
support, and usually more power, sometimes the "get what you pay for"
doctrine doesn't hold true. For example, there's absolutely no reason to
spend $10k on an amp. But some people do it - at least in home audio.

I do understand how
amplifiers work and specs don't always tell the true tale of what the
consumer is buying or how it will sound. I don't believe you can measure,
with instruments, how an amp will wound in the real world.

Why not?

It's like fine
wine - you can measure the alcohol content of two fine wines but can you
can't measure the fragrance and taste.

The only reason we can't measure the fragrance and taste is because we
haven't worked out the details of the human olfactory system. Very little
is known about it, in fact - MUCH less than the other senses. We do, however,
have a good idea about what aspects of sound humans can perceive differences,
and we can easily translate these thresholds to electrical and
acoustical measurements. Furthermore, we can in fact isolate the
amplifier as the lone variable and perform basic tests challenging
observers to tell the difference between two amplifiers. The key here is
isolation of variables - making sure that the only difference is the
amplifier. This requires careful level matching, assurances that both
amplifiers are not clipping, and that the experiment is being performed
double blind. You haven't done this, so quite frankly, this renders your
own personal observations useless.

I work in sensory neuroscience. I get a paycheck to investigate how people's
senses work, and the underlying theme throughout all of what we know
about human sensation is that the brain is NOT interested in accurate
reproduction of our surroundings. It's interested in only those
components that are important for survival, and in order to promote this
goal, it's devised ways to actually distort incoming information to better
suit the needs of the animal. The bottom line: you cannot always trust
your senses - not only do they have the tendency to deceive you; they're
actually DESIGNED to deceive you. As such, prior knowledge about the
audio equipment that you're using, misconceptions between sound quality
and accuracy, sound quality and loudness, etc. all lead to the perception
that system A is superior to system B, even if no difference is actually
present. This is why it's vital to remove these variables from the
equation when you're performing the tests.

I'll take my ears over your
instruments any day. No offense but that is how I feel. Please come over
with your Radio Shack amp and I will challenge you that I can spot the
inferior amp - every time!

Well, I don't have the time or desire to do it, obviously. But there's a
fellow named Richard Clark who has offered a $10,000 amplifier challenge
who will be more than willing to let you give it a try. Why not? If you
genuinely believe that you can tell the difference and you can pick your
amplifier out from the Radio Shack amplifier, you'll end up $10k richer.

Even at low listening levels. Cheap amps don't
have the same revealing amplification as a well made amp. And it's not
distortion that is the deciding factor. There are many other factors that
your instruments can't measure.

You've made mention of this a few times, but never elaborated. What is it
that instruments can't measure that could be responsible? Of all the
questions I've asked you, this is the one I'd really like to hear an
answer for.