Durable

>>Two things that justify extra markup is rarity and testing.

>>Because there is some increased cost associated with toughness, fewer customers will buy the product so the price must be even higher to compensate for fewer sales. Those customers that will buy it are looking for tough durability specifically and so the price may be higher because its a hard to find quality.

I think rarity is bigger factor than testing.

However I think also that something aimed at the durability market is also likely going to be treated far worse and have higher warranty claims.

That being the case I'm sure they are making higher profit margins on them. There are plenty of alternative materials that are cheap.

Tough plastics, Aluminium instead of magnesium and titanium.

Personally I'd love to see the tough models become the standard and the current models become the lightweights :p I'm sure plenty of other folks would like more durable laptops to be the standard.