Exactly! Why buy a new computer if you dont know how to use it?
How many people take their cars to someone else for an oil change? To do routine maintenance that anyone who invested a little bit of time in learning, could do themselves? Just because it's intuitive or easy for you, doesn't mean it isn't impossibly impenetrable for someone else.
Same thing for home repair. Basic plumbing. Carpentry. Sewing. All relatively simple tasks to pick up and learn if you look at it purely from a complexity issue, yet most of us have to hire someone to do these things for us.
A car is a black box to me. It gets me from Point A to Point B. I put gas in it to make it go, and I pay someone to do regular maintenance on it to keep it running for a while longer. To a lot of people, the computer is exactly the same. It's a black box that allows the user to accomplish certain tasks. The sorts of people who would want the Geek Squad installation are the sorts that probably use their computer for email, saving digital photos, writing the occassional letter and surfing the web.