MP, it depends on what you mean by Groupon’s business… after all, Groupon is but a mild variation of Priceline’s approach from 10 years ago. The difference, AFAICT, is that Groupon is pumping hundreds of millions of dollars into customer/user acquisition to keep the numbers that enable the Ponzi racket possible. Others could duplicate that of course, but Groupon’s management was probably the one with the biggest balls!
When FB and Google grow these services, they are more likely to do so in a more sustainable way and in a way that leverages their existing connections (to users, retailers).
My 2 cents,
—ravi