What CNNSMS is saying is true. I have 2011 335i X-drive and have very little brake dust. I can go weeks on end without washing (I can get very busy you guys so don't shoot me) and still have little dust. My wife has 2012 GLK and now that produces lots of brake dust. After 3-4 days, I feel like washing all the wheels.
2011 335i X-drive sedan 6MT/ BS/ ZSP/ Chestnut brown leather/ tint 35%/20%, Lux H8 V3