All companies have some sort of operating procedures which the person fixing his console would follow. Plus at least when I have had to take other electronics in to be repaired the item goes through 5-10 different hands. A piece of paper can be lost in that process ore orders can be watered down. Putting signatures on anything that might have to changes hands in the future is not the best place. Those signatures if he really wanted them would have been better off on a piece of paper or maybe inside the Box the Xbox 360 came with. While I do feel sorry for him what Microsoft did was not unreasonable.
Systems I own (Games)
Sega: Dreamcast (40) , Saturn (25), Genesis (50), Masters System (10), Game Gear (20)
Sony: PS1 (8), PS2 (60) , PS3 (5), PSP (12)
Atari: 2600 (18) , 7800 (10), Lynx (10)
