Why is there (supposedly) so MUCH difference in today's tube amps if most of them use the same tubes?

Most of the modern day amps use a combo of 12AX7s and 6L6s or sometimes EL84s to drive the amps tone and typically the same sized speakers (for example, two 15s or four 10s). Sure, some of the speakers may or may not be higher end. Celestions, I guess, are pretty sought after for clarity. Which leads me back to my original question, if most of today's tube amps (Mesa/Boogie, Soldano, Marshall, Peavey, Hughes and Kettner, Crate) have similar components, then why does everyone claim that they all sound so much different from one another. There are little nuances in sound that make them slightly different sounding, but really, at the end of the day are they THAT much different from each other?