Exactly.
Once you factor in rolling resistance from the over inflated tires, say, a dirty chain that increases the rolling resistance, different viscosities of oil, condition of the rear carrier bearings and preload on them, wind resistance, whether you are tucked in or hanging out all over the place etc, its really hard to pin it down.
Thats why when I see someone say they did 95 on a dyno I just kind of laugh inside.