I don't use groupon for restaurants or services because I'd probably hate it if I were in their shoes. I think business owners get roped in the same way that artists or programmers do free work because "it'll look great on your portfolio/resume".
These deals are reasonable to offer if your overhead is more than your incremental costs, for instance. Or if the look of a full restaurant (and thus the vibe) is more important than making money off of those initial customers.
The joke is groupon taking so much for brokering this. Groupon doesn't do anything to warrant $1 per coupon, let alone 1/4 the face value. If it takes off it'll be on ad-driven sites taking no or very little cut, and/or via the restaurants' websites and facebook pages directly.