I can speak for their terrible cheapness, I work at a repair shop and we got a lot of HP laptops. It's extremely common for the very stiff hinge just to snap the upper case because they didn't even try to reinforce it. Just 3 screws to hold down this half an inch long hinge and that's it, you can see it flexing and twisting when using it.
I swear all those HPs and frankly a lot of dells have the build of wet newspaper, I wouldn't touch them (minus HP elite books, my 8770w is great).
On another note Lenovos and Thinkpads are always very sturdy and are very good.