Well, when I'm looking at the seat of somebody else's pants who used to be looking at the seat of mine, that's pretty good indication that I'm going slower But of course it is all subjective. That's why I said, the science behind it sounds very convincing but...

It's also quite possible that the difference is small and for such a brief duration (such as when changing direction or accelerating hard) that it makes no practical difference on the road but is still detectable to the rider, resulting in that "slower" feeling.

edit: Just to show how subjective these things can be, I remember way back in the day the "fastest" car I ever drove was my buddy's 1965 Ponitac Grand Prix with a 421 tri-power engine. In truth it was at least a second slower than my or my other friend's heavily modified Z28 and Mustang GT but man was it scary. It was as big as a yacht and made a deafening roar when you cracked open the three two barrels. The softly sprung front end seemed like it wanted to come off the ground. You had to steer for all you were worth with the big manhole size steering wheel and all you could do was nudge the thing in the direction you wanted to go as the rear end fish tailed out from under you. And don't even think about stopping as the big 8-lug aluminum finned drum brakes were all show and no go, er stop. It was Mr. Toad's wild ride. You had white knuckles the whole time. IIRC it actually only turned 14.8 in the 1/4 mile but my God it was a beast. The Z and the Mustang turned 13's but were so well behaved by comparison as to seem tame.