For customers, Groupon adds almost no value. A great marketing deal will get publicized anyway - there are hundreds of websites devoted to coupon/code sharing. So if a business wants to offer 50% off, they could spend five minutes mailing a couple of these sites, and there would be plenty of publicity for their deal.
For almost all businesses, Groupon adds negative value. It costs money to fulfill these deals. "Losing money on every sale" is not a way to build a real business. The customers are the worst possible: solely money motivated, never going to do repeat business, and all coming in a giant surge which your business is not likely prepared to cope with... that's absolutely the opposite of the kind of customers you want.
Groupon has been able to paper over these problems with creative accounting and venture capital. This will not last forever.