The thing with Groupon is that it can't afford to keep it's implicit promise to merchants. It's a conflict over customer loyalty. If the customers become loyal to a couple of local restaurants, Groupon loses them and must 'purchase' new ones. If they remain loyal to Groupon's offers, then they will not be worth the merchants' expense to put out the offer. Based on this, Groupon must either keep spending to acquire new customers, or new merchants. Either way, the large marketing costs are here to stay (until they saturate the one market or the other and burn out). I don't think Amazon had any such fundamental conflicts to deal with.