The future (as seen by Steve Jobs)
If I had to guess what Apple is trying to do with the Mac Mini, it would be to get the thing into the living room to rule the roost.
Here's the system.
iTMS acts as the video-on-demand server to deliver video content to the home.
The computer in the home (Mac or PC, it doesn't matter so long as it has iTunes) is used to purchase content.
The Mac Mini, sitting behind a big screen in the living room, connects wirelessly to the computer, and, using Bonjour, access the content, and puts it up on the screen.
This effectively turns the Mini into a "tuner" for Video-On-Demand.
At the moment the price is too high for this to go ballistic. But then, that was the case with the iPod as well. The iPod rapidly became huge because people could put their CDs onto it. With VOD, we're going to have to wait a bit longer, because we have to wait until way more content is available on iTMS. As has been noted, there are still many popular TV shows that are missing.
Programs such as the evening news can be done as a video podcast, with the download being initiated automatically if you are subscribed.
I would expect that the price of the mini is going to drop in the future. It is already powerful enough to handle h264 at a decent resolution, so Apple won't need to keep boosting the specs.
All of this IS going to happen. VOD is just so superior as a viewing experience, that once enough content is available, most people will find the advantage compelling. The only question is whether Apple can leverage iTMS and iTunes to make the mini the receiver of choice in people's living rooms...