"We take no stance on RetailMeNot’s business model. (We like getting coupon codes too!) We also have no idea how the company achieved its SEO dominance. The company has no doubt put a lot of work into conquering Google."

The answer could be simple. As far as I know, RetailMeNot was one of the original coupon aggregators. (The domain was created in 2006.) It also seems to concentrate on natural SEO and does not seem to be cheating. Combine that with good quality content and you have solid SERPs.