If you compare the different form factors that are out there today ranging from smart phones to tablets, thin laptops, desktop replacement laptops there's one could classify these devices into two categories. Either it's a lean back device that is used most often for reading and consuming information or either it is a lean forward device where digital content is being created on.
This is he differentiator that drives both markets and that therefore a tablet will never replace a laptop or the other way around, they are both here to stay.