If anything it's to give people the incentive to actually flesh out a bug report and send it to them. I really have no idea where everyone's getting this "The black market will pay billions!" idea from.
Facebook is a closed system, an exploit there is worth precisely nada. Any use of it for monetary gain will be shut down fast and probably audit-logged to find you. Find an exploit kernel-level that allows you to execute any command you want at any administrative level on Windows/Linux/etc which allows people to drastically increase their botnet size? That'll get you some cheese.
