Within an A/V HT environment, I think "DIY" can be separated from setting up something yourself.
I wouldn't consider hooking up components in a HT setup a true DIY project, it's expected that a consumer would have to make the connection to interface that component with the rest of the gear. Otherwise, tying your shoelaces could be considered a DIY activity.
It's out of the ordinary to put together speakers (from an average consumer standpoint) from a cluster of parts, even in kit form. It's not out of the ordinary to expect someone to connect a DVD player to a receiver.
People do make their own amplifiers, though it less common because of the need for other types of tools and measurement equipment to make sure the parts are connected properly (else you risk things going up in smoke when you plug in the power cord to the electrical outlet). If you know what you are doing, you can build powerful amplifiers for a fraction of what an amp of comparable power would cost.
The same goes for pre-amps, processors, and other A/V source. The amount of test equipment needed to develop these components (and fabricate the components) from scratch would far outstrip the value of creating them on a small scale. It's an unreasonable expectation when discussing DIY projects.
DIY Speakers and subwoofers are much more tangible and achievable and affordable projects, especially if a proven plan is followed. The same goes for stands, and racks, and projector screens/walls.
