Most of the sales I've seen coming through from Groupon and Livingsocial feel like they could be impulse purchase material. Eliminating the second thoughts of a "confirm your purchase" page probably adds a nice amount to their sales, even if it's hard to quantify how much from the outside.
P.S. The transaction was likely not batched until much later in the day, from what I remember with credit card processing. Thus, undoing it would be trivial, if LivingSocial wanted to do it.