so it's not that the undergrads are particularly dumb - it's that expectation is often more powerful than experience unless you consciously control for it. for example, i suspect it's easier to detect the difference between coke + pepsi when you're given an unbranded glass than when you are given the two in branded bottles, but swapped (and, importantly, not expecting it).
The truth is that real experts can distinguish these differences - many trainees many not be able to, but that that's a different matter.
And as I've mentioned, I've been able to tell the difference between Coke and Pepsi even when all environmental clues (my order, my expectation, the type of glass) have told me that it's the other one. Again, it's highly likely that these environmental clues often influence people a lot more than they realise, but that doesn't equate to the claim that experts can't see through these either.
I agree with you 100% on the Coke versus Pepsi thing. Anyone who has spent much time drinking wine has wines they like better than other wines; there really are taste differences. (Note that I'm not saying more expensive is better; rather, that there are $15 wines I love, and $15 wines I don't like.)