From 1 brand to another, you can find an amp, preamp, speaker etc, that spec very close or in the electronic side, even identical.
I suspect, everyone listed above on this thread would hear the difference between the 2 amps, pre amps or speakers.
Based on that, I disagree with the blanket statement.
However, specs do contribute how amps sound and many could take 2 very differently spec'd amps (or circuit layout for that matter) and tell you how they in general would differ by what they see on paper.