duker, I agree with you, but I never chased that down as I didn't see a need to. The "feel" is ok as is, and the crosschecks I did with the HRM corroborated it. I must admit that the perception of effort on a TM vs track at higher speeds is a little "strange". The TM is strict. That is, the TM "forbids" you to do the equivalent of slacking off a bit on the backstretch and making it up down the front. Although, if I were to do something like 5x1200 at 5k velocity, I'd be equally tired at the end of the workout whether on the TM or track. That's another of my gauges (and the primary one I use if I have to crosstrain due to injury).
I wonder what it would be like to run on a huge treadmill, something like 30 feet wide and 100 feet long, so that you could play with your instantaneous velocity a little. Not that it's at all practical, but I wonder if the lack of spatial constriction (mental effect plus the moment-to-moment speed variability) would account for differences that have been mentioned by some.