The answer I got was...
Due to the fact that the rod bearings are needle bearings there is more clearance than in babit bearings. The extra clearance is necessary so the needles don't get in a bind. Free revving a 2-stroke above 2000 rpm with no load causes the bearings to get hammered and can ruin the bearing surface on the big end of the rod. I am not sure if it would ever hurt the wrist pin bearings as they are not turning at the same velocity as the rods at the crank. I found some good info on this topic on screamandfly.com.
I have personally seen many more rpm on my engines than 2000 out of gear. I don't think I ever hurt one by doing it but I won't take that risk any more.
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