I think the issue here is simple bias control. There's definitely a tendency, whether consciously or otherwise, to hear what we want to hear. A blind comparison is a very useful tool for assessing differences or non-differences between components, formats, et al. I've caught myself before believing that I heard a difference when actually nothing had been changed in my setup.

I also recall similar tricks done by some high end audio manufacturers. A few years ago, Wilson Audio demoed a new speaker system using an iPod as the source. But, they'd first put up this elaborate looking test rig, so the audience didn't know they were listening to those high end speakers through an iPod.

At high end audio shows, Dunlavy and McIntosh have also pretended to swap out speaker cables to make a point about exotic cabling. People would swoon about the "night and day" difference that the cabling made, only to find out that nothing in the system setup had changed between listenings.

With wine tasting, I've definitely seen how preferences and expectations will often boil down to the price point. When you put the blinders on, then it really tests just how good someone's purportedly well-trained taste buds are.

As T mentioned, this is not necessarily an assessment of preference, but rather of reliable comparison. And whether we admit it or not, I think we all have some biases that need to be controlled to some extent.