The DF article said they sold 503 devices "before they pulled the plug." I'm sure MS didn't go around getting all the un-sold devices back from vendors -- they continued selling their stock. It's just that 503 devices were sold when MS decided to kill the program.
Yes. Unless this is going to be one of those "Atari 2600 E.T. cartridge" situations -- where you find a reason to dig a giant hole in the desert and bury all your warehoused stock -- every Kin that was manufactured is going to end up being turned on somewhere, somehow, at some price. And surely they manufactured far more than a few thousand.