Not really sure why they would put serial numbers on bike components, but they seem to do this on many higher end ones.
SSC deraillers from Mavic have their own little individual serial numbers stamped on their bodies, but what difference does it make in Mavic's instance, as you can practically replace everything on it anyway if needed. I think the companies just use the whole individual serial number thing to give them a little bit of bling factor.
Just to make it wierder, I just aquired an NOS Mavic 851 SSC derailleur set, with everything on it totally new and clean/unused with no signs it had ever been dissasembled.. It even has what seems to be the original grease applied at the factory........but there's no serial number on it for some reason. Same goes for the FD that came with it......Hmmmm....was this some sort of unserialized prototype/bike show set??

Chombi