No mention of Woot and the other original "daily deal" sites?
Maybe Woot is the post-Groupon. After you Groupon'ed your business to death by slashing your revenues 75% at a time, folks like Woot get to sell off the skeleton. As long as businesses keep failing and inventory management keeps sucking, Woot will have plenty of business.
That's actually a thought though: a lot of liquidation inventory comes not from outright failing businesses but just really poor demand forecasting and logistics. With improvements in these fields Woot may find it harder and harder to source compelling products.
Or it could go the other way! Woot seems to have no shortage of goods to liquidate (notice the proliferation of "sub-woots", like "woot tshirts") so perhaps as demand is better forecast, quantity of surplus of any one good will decrease, increasing the variety and decreasing the amount of time any one item features on their front page... which could be very good for them.
I actually thought that's what the article would have refereed to as well, but as far as I'm aware, Woot! and similar sites are doing just fine. Woot! in particular is owned by Amazon now and has several dozen "daily deals" open at any given time now.
Edit: "The deal-of-the-day concept gained popularity with the launching of Woot.com in July 2004, although Woot itself was a modified version of earlier dot-com bubble sites such as uBid. By late 2006, the deal-of-the-day industry had greatly expanded to over 100 deal-a-day sites. In November 2008, Groupon entered the market and became the second fastest online company to reach a billion-dollar valuation.[2]"