I don't think Jobs was so much opposed to geeks tinkering with their toys, rather he wanted a computer perceived as a solution providing tool for everyone, not as a problem in itself usable only by engineers.

Is there more information about Steve Jobs actively being replaceable parts for business reasons? My impression is that it's one of the first things to compromise on for cleanliness, but there is not directly a design culture against it. The Powermac G4 seems like it was easy to service.

Of course it's very easy to imagine that bad serviceability is encouraged by some managers.