The 9 tailed fox is also stated to have infinite chakra at one point if I recall. The statment doesn't mean much because infinite is clearly not a thing in naruto. Especially if all that is required is a moon sized seal. As for Sora? https://www.youtube.com/watch?feature=player_detailpage&v=gB2RpcRnhn0#t=100 Does this look like a normal human?