Just about every brand/dealer has some sort of oil change special and are almost always cheaper than you can buy the parts/materials yourself. They use this as a loss leader to sell other work. Once the car is in the air they will look for other work to sell you, including the "60,000 mile check up" for $299+.
I don't disagree with the approach because fixing worn parts before they break is always easier than having them break on the road, especially when you are towing. Just be careful of what you're buying...
Also ask if the oil change includes a lube if you have greaseable fittings on ball joins, tie rod ends, etc.
