OK, i have kicked theis about for a bit and here are my thoughts. Could be true, part true, pure WAG, but I can see a few points that would make a tire maker nervous, especially one with as poor a track record as the stones.
1. any misalignment could cause a biased wear pattern that would buggar handling for the next few hundred miles.
2. Running up to full power in top gear without any air induced drag to slow the bike could easily excede the max speed rating of the tire and start it breaking apart.
3. Running the rear wheel to max power (therefore max load and speed) with the bike standing still could result in exessive tire heat that may start the tire breaking apart. While they usually have some sort of fan or blower keeping the engine cool, it doesn't necessarily cool the tire as much as real air flow might.
Now, unless you are on the salt flats, you would usually be varying the power quite a bit to avoid crashing if you were actually riding. On a dyno, on the other hand, it's just power up to max, hold it whilst taking some readings and maybe tweeking a few adjustments, and then shut down, so I can see the overheating thing being a real factor.
