Customer serviceable and easily repairable are two different things.
Can I buy a new compressor for my refrigerator and install it myself? Yes. Is it easy, and would the vast, vast majority of people who own them ever do it? No. Why? Because they don't have the proper knowledge, training, diagnostic or servicing tools. Plus, the appliance is considered a sealed unit to virtually anyone who would buy it.
Now think about that in context of an iMac, or even a MBA. Can I buy a new internal part for it and install it myself? Yes. Would the vast, vast majority of people who own them consider doing it? No. Why? Because they don't have the proper knowledge, training, diagnostic or servicing tools. Plus, the computer (aka appliance) is considered a sealed unit to virtually anyone who would buy it, small, vocal geek minority excluded.
We are in a transitional phase in computing. We are going from the point in time when computers (including, but not limited to desktops, laptops, phones and tablets) were considered hobbyist devices by many, to a time when almost everyone will view their computing device as just another tool in their lives to get things done. At one point there was an argument for making computers serviceable, because technology was relatively expensive, and the power of available hardware was constantly being challenged by even the most mundane of tasks by even the most basic of user. The ability to upgrade from 16MB to 32MB of RAM, so that your computer wouldn't crash when you tried to open Wordperfect and Lotus 123 at the same time was desirable, and logical.
Now you can buy a computer that will do everything that 99% of users need it to do for the entire realistic life of the computer. Do parts fail prematurely sometimes? Yes. But I don't hear anyone grousing about their KitchenAid blender's motor burning up, and not being able to open it up easily to drop another one in.
10 years from now a new generation will be amazed that there was a time when people opened up their computers to throw new parts into them.