That's easy to say, and not always easy for everyone to do. Not everyone is mechanically inclined. I know my share about my computer, but when it comes to anything internally, I wouldn't feel comfortable enough to do it. I'd hate to break something or make it worse.
I'd say that is a very fair assessment of around 95% or more of users. Most people are just happy if their machines works as intended its that smaller percentage of us that like to fix things ourselves or build new machines from parts.