There's Visual Website Optimizer and it's competitors. I've made good money in the past by setting VWO up on client websites and handling their testing for them. They aren't interested how it's accomplished or whether it's a software or service solution, only that before I started they sold 10x widgets a day and now they sell 15x. When x is worth several hundred dollars it makes them more than happy to pay good money for it to be done.

I suspect this is true for all but the tiniest of companies.