Actually, they own patents on the pin-out for the 30-pin connector. They probably own patents on the 9-pin as well. Doesn't really matter if the patents are enforceable, the threat of a lawsuit versus the cost of the license keeps manufacturers from being too ballsy - do you risk your entire margin (or more) fighting Apple over pin-out licenses?

Also, if your accessory is not "approved," then it stands a chance at voiding your customers' warranties. That'd be bad for your business.