Hi Glen,
I noticed that while I was rotating the distributor the RPM of the engine doesn't change significantly as you mentioned about the ECU take care of the timing by compensating it, this seems to be true.
However, I believe that the distributor position is essential to the ECU as it calculates how much to compensate. And if the distributor position is at an optimal position then the ECU would be much accurate in its calculations.

Just a thought
Alex