Here is a simple exercise anyone can do.
Take a piece of cardboard, not a cereal box, proper cardboard. Cut one to the size of a MacBook Air screen, cut another to the size of 17" MacBook Pro screen.
Take each one. Place this so the board is parallel to the ground and place your index finger under the centre. Each one will bend in the middle due to tension. The Air sized will be more rigid. The 17" one will sag. Now imagine making a screen as thin as the Air for 17" laptop. If you try and close it by only moving it from one side, it could damage the display. Would you be willing to put up with a failure point so obvious that the industrial designer who thought of it should be shot?
So we now have a laptop with a very thin fragile display, let's get to work on the main case. oops. We need to throw out the Superdrive as it is going to be too thick for the case at 0.8". We demand Sony build us a one off DVD/BD drive that 0.3-0.5" thick, but spins at 1600x. HDD. To big, or we use the really low capacity 80 gig 2.5" drives. CPU. Down from 2.5Ghz to Maybe 2.2GHz at most with CPU throttling. Heatsink and Fan cooling would be need to be redone completely. Making them smaller would make them less efficient. They would have less surface area. Can't just dissipate the heat through the metal. The case would get too hot and possibly warp.
Take a piece of cardboard, not a cereal box, proper cardboard. Cut one to the size of a MacBook Air screen, cut another to the size of 17" MacBook Pro screen.
Take each one. Place this so the board is parallel to the ground and place your index finger under the centre. Each one will bend in the middle due to tension. The Air sized will be more rigid. The 17" one will sag. Now imagine making a screen as thin as the Air for 17" laptop. If you try and close it by only moving it from one side, it could damage the display. Would you be willing to put up with a failure point so obvious that the industrial designer who thought of it should be shot?
So we now have a laptop with a very thin fragile display, let's get to work on the main case. oops. We need to throw out the Superdrive as it is going to be too thick for the case at 0.8". We demand Sony build us a one off DVD/BD drive that 0.3-0.5" thick, but spins at 1600x. HDD. To big, or we use the really low capacity 80 gig 2.5" drives. CPU. Down from 2.5Ghz to Maybe 2.2GHz at most with CPU throttling. Heatsink and Fan cooling would be need to be redone completely. Making them smaller would make them less efficient. They would have less surface area. Can't just dissipate the heat through the metal. The case would get too hot and possibly warp.