The Mac mini's end is near. It would cost too much for it to take advantage of OS X 10.5 the Apple TV has replaced it in many ways or will.
YouTube is the mp3 napster of the video world, the Apple TV is the true video iPod.
Features from the Mac mini and the iPhone will start to trickle into the Apple TV as it upgrades. The goal will be a living room media center that can be simply controlled with a remote or hand gestures. Beating Microsoft surface to the punch.
Consider the evolution of the iPod and the iMac. Apple's philosophy is to use older hardware in a pretty package with easy to use functions. It begins as a striped down version, and slowly adds old features that seem new. ex. the iPod, late to the mp3 player scene, the iMacs stripped down, no disc drives etc., iPod Nano, same as the mini but with less memory, the iPhone has limited memory and no support for 3rd party software, the Apple TV again limited HD space slowly increasing with upgrades.
On a side note I'm curious to know how the Apple Hi-Fi is doing, I had to look it up because I forgot what it was called and then had to look for it on the web site, hidden away.