Why are xi brake jobs different?

I just got my first BMW today. It's a 2003 325xi. It seems solid so far with the exception of being way past due on a brake job and having condensation in the headlamps.



I was reading the manual tonight and it makes a point of advising that xi brakes be serviced specifically by BMW because the rear installation is different and damage could be done?



What exactly is so exceptional on the rear that makes it different from any other rotor/pad install?



Thanks for any help!