You don't quite 'get it'. The headless Mac isn't for you, obviously. Its a huge step Apple is taking to leverage the halo effect from iPod sales, getting windows users to switch. These people don't need 3ghz G5's.
Yeah, its a pretty huge deal. I have no need for one, but I bet almost each of us here knows someone who would really benefit from the OSX experience who hasn't before had the pleasure, and now it will be affordable. But from a sheer risk/reward prospect, Apple is taking a big gamble by making such a machine. If it fails, they are unlikely to consider doing anything like it again for the next 20 years. A larger user base means more developers, which means more software, etc etc. You just might end up indirectly benefitting.
Now, if a competitor were to someone have all of this information in advance, including what the machine looks like, they could have all kinds of material ready on launch day to announce something 'better' (even if it doesn't exist yet) to counter the Apple buzz.