Where's the "popcorn smiley" when you need it?
There are few things that come to mind for me (and I neither have "golden ears" nor I am a general believer in the more esoteric "tweaks" out there--I don't use exotic cables or power cords, for example).
One--I'd like to know what discs were used. The biggest theoretical advantage of hi-res for 2 channel, in my opinion, is the greater available dynamic range (though the audibility of that, all other things being equal, is obviously a point of contention).
Two--I suspect that much of the better quality audio in hi-res owes something to the fact that, generally, those that go to the trouble of releasing in hi-res take extra care to do it right. Far fewer instances of overwrought dynamic compression (a HUGE culprit in the last decade of redbook releases overall), fewer egregiously gross applications of unnecessary EQ, and so on. So while redbook CD MAY (I'm not concluding anything, just stipulating for discussion) be "as good", the people issuing redbook are NOT making the necessary effort for the practical result to be "as good". As such, I will continue to buy hi-res when it is an available option.
Three--and this is purely a personal preference, I buy hi-res PRIMARILY for MCH presentations. Redbook CD is not capable of providing me with that in anything other than a lossy DTS-like format and I can most certainly tell the difference between a lossy DTS-CD and a hi-res lossless presentation of the same mix (I've done a level-matched comparison). As I am a big fan of MCH (discrete) mixes, I will happily buy a lossy DTS-CD version if there is no lossless version available, but I will always privilege the lossless option.
So, this is interesting (and, perhaps, not all that surprising) but as MCH is my preference, this study's conclusions will have no bearing on my hi-res purchases.