Adversity and scarcity breeds a precision and a ruthless attention to detail that prevents that $50 from escaping. Meanwhile abundance leads to a relaxing of all such, and maybe even a dulling of that skill. Being born into wealth I imagine would put you at an even bigger disadvantage in that regard... though I might be okay with having such problems...
[0] I'm paraphrasing of course and I changed Law to Economics. http://www.bartleby.com/73/1002.html
Without that added utility, saving $50 alone might not be worth 30 minutes to them.
Let's make it more extreme. A $50 item for free or $50 off a $5000 purchase. Discounts as big as 100% off don't come every day. Maybe you'll never see that deal again in your life. You should jump on it. Where as a 1% discount is something you see every day at dozens of stores. There will probably be a bigger discount next week, so don't bother going out of your way.
If you have to make a choice between the two, you choose the item with the less-common discount.
But that's not what the study asked. The study said "you need to buy this item now, where will you buy it?" In this case it is illogical to prefer the higher percent discount, dollar value is the only thing that matters.