Having said that, getting grips too early can be nagative (our girls got them too early I think). They may not learn to grip the bar correctly if they go straight to dowel too soon, and some of our girls I have seen struggle with this. Grips also have the potential for causing damage to the growth plates in the wrist if used to young. But then again they are much harder to introduce later on when the girls really start to need them more and can be easier to get used to early on.
I am curious about this... I wonder if the issues are really grip related. All of our gymansts get their grips early - my dd when she was 5, with very tiny hands. They all learn their basic bar skills to advanced bar skills in dowel grips. Our gymmies ALL have great bars - and never any wrist or hand problems. I wonder if you have any info to back it up, and if so could it be grip "brand" related?