It's a real estate company because for many franchise stores, it owns the land and collects rent and franchise fee from the franchisees.

“McDonald’s real moneymaking engine was its little-known real estate business, Franchise Realty Corporation; envisioned and created by Harry Sonneborn. The obscure McDonald’s alter ego company was based on Sonneborn’s unique even lesser known financial formula.” http://en.wikipedia.org/wiki/Harry_J._Sonneborn (First CEO)