I'm not sure about the soft rotors theory, but after having changed pads myself at least 40 times in my life and dealt with numerous dealers here what I can say on the topic.

1. The bottom line is that once the rotors are below minimum spec they are no longer recommended to be used safely. The thinner they get the hotter they will become when stopping the car. You eventually run the risk of overheated brakes. Plain and simple.


2. The calipers have plenty of space to push thin pads onto thin rotors. Just make 100% certain that you have enough brake fluid in the system/reservoir for this to happen!

3. Under the free maintenance plan BMW always changed the pads and rotors together in my experience.

4. Front pads/rotors obviously wear faster than rears. I've measured very accurately the wear rate on my front rotors and extrapolated the mileage I would get out of a set of rotors. With mostly highway driving I can usually get away with changing rotors on every other pad change, with one very big exception below.

5. Because the pads eventually 'bed' into the rotors they seem to make a channel or groove in the rotors that gets deeper as they wear down. From my own experience, YMMV, the outside edge of the rotors always develop a 'lip' that is significantly higher than the surface that the pad has been contacting during braking. After having discussed this issue with BMW NA and several BMW Master Technicians this scenario is not recommended for a simple pad change because the new pads will not simply pop into the pre-existing wear channel and end up making less than 100% contact with the rotors. BMW feels this would significantly increase braking distances and so they do not recommend a simple brake change for reasons of safety. If your rotors, as measured in the channel, having plenty of wear left on them then you could take them off and have them machined to be perfectly even (you can get this done at a local Pep Boys for example) and then you are good to go. Because it's a huge pain to put the car on stands, drive dirty rotors to Pep Boys, wait for them to be machined, bring them home, install them again I have generally opted with simply putting on new rotors. One alternative is to put new rotors on and sometime later have the old set machined to be used for the next change, but this is more work than I have time for these days.

Anyway hope this helps.