All my friends who do paleo eat plenty of carbs, just not crappy carbs.
As for assimilation most diets heavy in protien, especially from meat are hardly 98% assimilated. The body simply doesnt have the digestive enzymes to handle large protien loads which means a lot of it sits in the intestines rotting...which of course causes toxic buildup, gas etc.
My biggest grip with paleo is that the food choices, especially considering individual food preference, is very limited which means a well balanced diet is impossible and ample supplementation is required.