Because the market is so competitive, the moment the engineering teams gets 8 hours of battery time (life is another issue) then the market forces that battery size to be cut in half or more to drop the price of the unit.
To get more time, see if larger (more cells, more mAH) batteries are offered.
Looking for a laptop/notebook/tablet. Main criteria is that it be small and lightweight with the longest battery life. Don't want anything that will be outdated soon. Am willing to go heavier for best machine. Any ideas??