[mpat]

The analysis makes sense on a micro level. To any one consumer, it is possible to prefer one bundle of goods (groupon quantity at groupon price) to another bundle of goods (standard quantity at standard price) even though the first bundle lies outside of the individual's demand curve.

However, relative to the quantity desired by any one consumer, the number of units required to activate the groupon deal is quite high. The pressure any one customer feels to buy more to ensure that the deal is activated would be negligible. I would expect that the number of units sold at the groupon price to coincide with the market demand curve.