Hank,
I was going to post pretty much what Ken said. "Group rates" doesn't just mean a traditional group of friends. Travel agents, including the consortiums and big box stores, can put large slots of rooms (not specific cabins, just types of cabins) on hold at a discounted "group" rate with amenities. They then sell those cabins at a discount with those amenities. The discount can be deeper if they include the "free cabin for 'x' amount purchased" in their math.