Weelll,
Unless you're flying a taildragger jet, then the change as the pivot moves from main gear to CofG at liftoff actually tends to cause the pitch rate to increase! This is due to the tail arm increasing. This (increased pitch rate) effect is quite noticeable on light straight wing aircraft, so I suspect that the reduced rate is a ground effect result. Since it also noticeable on the T-tail types I fly, it may be due to the sweep causing the wingtips to get closer to the ground during rotation rather than just plain speed.
Interesting though
