Amazon books revenue when someone orders a product, even if that product is "fulfilled by" a different merchant behind the scenes. Some people think they shouldn't be able to count that as revenue. Intelligent accountants disagree with one another.
Accounting is hard. It's rarely black and white. Anyone who was seriously interested in buying Groupon knew what their business model was (collect X from consumer, give X/2 to merchant) and this restatement won't change anyone's informed opinion.
http://phx.corporate-ir.net/phoenix.zhtml?c=97664&p=irol...
In 2010, they say "Generally, we recognize gross revenue from items we sell from our inventory and recognize our net share of revenue of items sold by other sellers."
(Page 19, the second paragraph)
portman's comment could still apply to sales where Amazon acts as the merchant instead of just the storefront.
And it's precisely because the SEC read the fine print that Groupon continues to have issues surrounding its IPO. It's their job to read the fine print.