I think the stability of the laptop case is important for long term durability.
My old MacBook Pro had this aluminium unibody and after 6 years was still working flawless (after traveling with the MBP a lot).
I also had some normal Laptops (Toshiba, Lenovo, HP) without a unibody. And they was much more vulnerable to traveling.
I think that the unibody prevents that the electronics is worn out compared to a normal laptop case.
That does not mean you need to buy a MBP, but to look out for unibody laptops they appear to be much more robust.
Maybe Acer....
Yes you are right @asknbid, exactly as you say. sturdy body like aluminum is very good for laptop. In addition to sturdy and strong aluminum also accelerate the release of heat on the laptop. I myself use HP Probook laptop that the top of the casing using alumunium material. But keep in mind, that the cause of the most vulnerable damage is moist dust and excessive vibration when the laptop is active.
@aziali "...accelerate the release of heat on the laptop..." also true.
HP is building good laptops (better than Lenovo imo), but the Probook has no unibody, or?