It's gross revenue rather than net. Take 50% off the top for paying merchants. Then the expenses you mentioned (sales cost, software design, hosting, etc.).
My guess though is that their major cost is customer acquisition. That seems to be the norm in this space. They're buying customers for $5 and making $2.50 off them (numbers theoretical, as an example) hoping to make the rest back later when they've won the market.
Groupon changed from "gross revenue" (which did not deduct money paid to merchants) to "net revenue" (which did). I believe they did this willingly because they were going to IPO, not because they were "slapped" or due to GAAP.
Living Social is private and can do whatever they want, but they probably are using net if they're comparing themselves to Groupon. Otherwise they're making themselves look half the size when they are really a quarter, which I suppose could be purposeful.
My guess though is that their major cost is customer acquisition. That seems to be the norm in this space. They're buying customers for $5 and making $2.50 off them (numbers theoretical, as an example) hoping to make the rest back later when they've won the market.