I think what is particularly interesting about the data surfaced in this article is the baseline prices from Groupon et al are so grossly exaggerated in this particular vertical (service industry).

For the service industry in particular, hourly rates can vary drastically by geography and type of business, whereas for spas, restaurants, or other store-front businesses, it's clear whether or not you're getting an actual deal/coupon because you can compare the deal to the base menu or pricing packages.