You only buy a house once, you buy chocolate bars all the time. $100 on a chocolate bar every time compounds.
You can find silly faults with individual examples all you want, but studies indicate that people have a tendency to think percentage-based about savings rather than absolute terms.
Which sounds like the smart way to go about it.
It seems a little illogical in the chocolate vs laptop $.50 off voucher, but it too makes sense. The laptop voucher provides almost no value to you, considering you are about to spent $700 dollars on the thing anyway. $.50 could be just the gas to go to the store to buy it.
$.50 for the chocolate on the other hand, will be taken only by cash strapped people (or coupon maniacs).
I doubt people with $700 at the ready to buy a laptop would at the same time clip a $.50 coupon for a chocolate bar.
Which also makes sense. $100,000 to me is serious money. To Bill Gates it's small change. Money is a relative - percentage thing.
A $20,000 car is a purchase you make once in 5-10 years. Saving $100 means nothing in that context --you're already parting with 200 times the amount, so if the $100 amount meant something for you, you'd have gone for a cheaper, say $15000, car in the first place...
Savings of $10 (20%) on small items, like food or garments, on the other hand, pile up.
You spend more than $20,000 on small items per year than you do on cars...
This isn't rational: they're clearly not buying the 100 gallons of gas for the gas-drive to make sense.