Hi,
Two reasons come to my mind, why I wouldn't reveal the serial off my devices, especially on a thread discussing how to hack it, too unlock features:
1) in case of a fault, the manufacturer could refuse warranty, based on the hack, which would be easy to prove had been done
2) if reselling the device, as a purchaser I wouldn't want a device that not only has been hacked, but had the hack announced to the whole world
Regards,
Vitor