If you don't believe that an amp, dac, cables, or anything else makes any difference, how can you believe that different models of headphones makes any difference?
Blind tests have also "proven" that people can't tell the difference in different prices/models of speakers either. Headphones are just speakers closer to your ears.
And plenty of people on Head-Fi say lower models sound better to them than higher ones. If there's any kind of difference, then some people will be able to perceive it, and then those people might have an opinion on which they prefer.
I think blind tests often take too much out of the equation, or leave variables in. Like blind wine tastings, $2 bottles beat out $50 bottles. So by that test, there's no point in paying more than $2 for a bottle of wine.
But "taste" is really made up of both smell and taste. When you have a cold it's really hard to taste anything, because smell plays a huge factor in taste. Why aren't blind taste tests done with your nose pinched shut? They're allowing another sense to change their perception in the test.
Audio can be a multi-sensory experience.