Only partially right. If you're using the spell Fly,  (http://www.d20srd.org/srd/spells/fly.htm) you're correct. For creatures with inherent fly speeds (http://www.d20srd.org/srd/specialAbilities.htm#fly), it's light loads only. I think there's a feat out there that increases it to Medium loads, but that's not standard. I can't speak for Kazumi, but Mark is definitely in the second category, because it's using Fell Flight.