looks like one is "bulk", probably their note for OEM, means it comes without cables and other accessories.
The heatisink is different. The HD-W30GLFS is the older model, and the W30HLFS is the newer one. The heatsink was changed to allow sever mounting of the drive (as in some server HDD rack setup the HDD slides in rather then connect 2 cables by hand like on a desktop PC).
What goodbytes said and the hlfs is a revision that moves the sata connectors to the bottom of the hard drive where they would be on a normal 3.5" drive. On the GLFS they are right on the middle.