^ that would be anecdotal evidence at its best. A small sample size it appears as I've seen several that are quite different. Please read this for the difficulty at measuring frequencies higher than 4kHz. Basically you get different plots with the exact same pair:
http://www.innerfidelity.com/content/expert-tests-innerfidelitys-headphone-measurement-repeatability-and-reproducibility
http://www.innerfidelity.com/content/expert-tests-innerfidelitys-headphone-measurement-repeatability-and-reproducibility