A fair point, but in all things there's a strong economic incentive to claim that a product does something it doesn't, if that will make more people buy it, and yet most things don't claim do do something which is simply factually not true.
Usually when it's a feature that either works or doesn't - so it's not a subjective measurement - it's likely that a product does at least technically do what it says it does.
Presumably the argument is that the manufacturers aren't specifically claiming a particular feature, but the disk is behaving in a particular way that just happens to be not what the user expected - so they're not technically lying. This does seem to weaken the idea that they're doing it to improve the chances of people buying it though, if they're not stating it as a feature.
Just out of interest, I've just spent a while trying to see if I can find out what the difference is between the Samsung HE502IJ and HD502IJ - two drives which are identical on paper, but one is sold as 'RAID-class'. Neither are even remotely expensive enough not to lie about their actions, so what's the difference? Well, some forum post claims that one has a 'rotational vibration sensor', whatever that means.
In conclusion, people who try to sell you things are all liars and cheats, and I intend to grow a beard and live out the rest of my days as a hermit, never having to worry about these things again. Perhaps I shall raise yaks.