Everyone is different, no doubt about that. You are right that on the highway, you will be hard pressed to hear a difference, but I guaranty, if you are ripping original CD's to MP3 at 192 or higher, there is a drastic difference in quality, that is very noticable at less than highway speed. At least with my set up with 4 - 7.25 Rokkers in the fairing and lowers, and 2 of the matching Rokkers in the back with an extra 250a running the fairing, and the stock 160 running the other 4. As a matter of fact, there's a considerable difference between the Std iTunes downloads and 192K MP3's.
Again, I'm not trying to talk anyone out of buying XM. I mean, what's $10/Mo if you already have the system that comes standard with our bikes. If you are happy, who's to tell you different? My wife can't tell the difference between FM radio and a 24K/44Hz Surround material on my high end audio system at home, so to each their own. However, the point remains, if you have the ear for it, and the equipment to present the differences, it's absolutely there. Your mileage may vary.
If anyone wants a demo of the various bitrate formats, bring a few beers and mosey on over!
