[mrbill]

I've never found any evidence that velocity does anything in-game up through v6.5, but as these guys link to, Markus has said it influences development positively:

Difference Between Stuff, Movement, and Control

That's the "velocity does nothing for Ks" study that is pretty solidly done.

I'd be surprised if any velocity effect was included in v2006 more than it had an effect in v6.5.

It makes sense that pitchers develop slightly better stuff (which is merely getting strikeouts) if they have higher velocity. But, stuff is the rating that matters in-game, velocity is a modifier on its development.

There's no reason to have two ratings describe strikeout rate when one rating will do the job.