Raul, Stylus drag does affect platter speed. I am sure the the effect is small enough that it would be extremely difficult to measure. There is plenty of evidence that suggests that it is audible, but nothing that I would consider proof. A scientific measurement would be interesting but would tell us nothing about audibility. Only our ears can tell us that. The problem is that there is no practical way to remove the affects of stylus drag without changing other system parameters. So it is unlikely that we will see a definitive answer to the question anytime soon.
I see the issue of stylus drag as a well grounded theory because there is plenty of empirical evidence that supports it.
I see the issue of stylus drag as a well grounded theory because there is plenty of empirical evidence that supports it.