Well, you may not be missing anything for how you enjoy the sound system, but for me it is missing a very basic simplicity. In addition to what Sarcastic6 said involving distraction, I use the sound system as follows.
1. Hear a song that I don't want to hear, change change the channel.
2. Hear another song I don't want to hear, change the channel. (etc)
3. Finished with these presets? Yep, hit the media button and cycle through the next.
4. Finished with those? Yep, hit the media button and cycle to the next set of presets (perhaps it's FM).
5. Continue in this fashion until I hear something I want, regardless of the source.
There are at least three one-step ways to change the station (1. The preset buttons on the stearing wheel, 2. The CD buttons on the dash, 3. The tuner knob.) but not a single one-step way to cycle through the media. I would argue that the media button would probably be one of the top buttons to be used in the car when it's in motion.
By posting this I was hoping that someone would point out that I was missing something simple. One could always hope that a software update might allow you to somehow use the quad button on the right side to do this in one step.