Agreed, even if Mercedes did want to hamper Hamilton, there's no way they'd do it in a way that's so spectacularly embarassing for the company.
I think Hamilton just intrinsically has bad luck. Remember back in the McLaren days, how people were constantly saying the only reason Button was close to Hamilton was that Hamilton was getting so much bad luck. It's probably his greatest weakness as a driver. Maybe he dropped a mirror on a black cat or was the victim of a gypsy curse or something. If it carries on like this, Mercedes will probably start thinking about dropping him and hiring someone luckier.