When someone treats a laptop like a book...it breaks. Especially because the cases and hinges are way more delicate than they should be and the little knocks add up and wind up cracking the cases two years down the line, and then once the cracks start everything seems to go.
Personally I try to treat my laptop like a sheet of glass, and even then the wear catches up. If I was doing it again for the long term I'd give serious thought to the Toughbooks that are "armored" (they aren't all) because gel-mounted hard drives and rubber corner bumpers CAN help protect it. It might be cheaper to buy a cheaper laptop and just replace it twice as often, but that also depend on how many hours (days?) you'll need to spend reinstalling software and user preferences. To me, THAT'S the real price of replacing a laptop, the time it will take to prep the new one.
A lot of vendors (from Dell, who I call Dell Hell, to Lenovo, who bought out IBM) will offer you a 4-year total "bump drop and splash" warranty on a laptop and that's also a good way to invest in protection. From the maker, these extended warranties are often only $300 or so to extend the basic warranty out to 4 years of total protection, although many stores will try to sell you a third-party warranty that does less for a higher price. (They're trying to make profits--by cheating the customer.)
If your laptop is not mission critical, and you won't mind taking three days off to reload software and set it up again...by all means, cheap and and replace it every 18 months instead.
And meanwhile, treating it like glass instead of luggage, helps them all.