I agree, especially from reading up on the A/B comparison thread. Like I mentioned before, I'm willing to bet the differences are mostly based off the amps own sound signatures and not how well the headphones are being driven (talking about the ones known to capably handle hard to drive headphones.)
In case of transparent amps, the differences are even harder to discern, to the point where once a headphone is fully driven, there's gonna be very little gain by going from one amp to another.
But of course, I don't own $2000 amps (nor will I EVER). I'd rather spend that money on headphone with different sound signatures, instead of trying to improve a headphone by 2% for $1000 more.