i thought what they said was generally true. the rotors are bigger usually in diameter and thickness so often heavier. the calipers are also usually of larger size but of lighter weight material. Pads end up being heavier as well because they are larger covering a larger swept area. you get more thermal capacity and larger stopping power with a slight weight loss. there is a thread comparing weight of each kit somewhere here.
02 Tiag e46 M3|6MT|GC plates|MCS c.o.|GC bars|GC race control arms|GC bushings & bearings|BW eng. & tran. mounts|subframe kit|BW race shifter|BW Jaffster|Euro header|BW race|K&N c.a.i.|Epic race tune|Rouge pulleys|Seibon CF hood|CSL bumper|ST-40|XR-2|SS lines|half cage|Recaro profi|Profi 2 harness|BMWpedals|BW studs|