They use Toshiba drives and here's what Toshiba says about it:
Region Protection Coding (RPC) of DVD Discs is a feature that is supported on DVD Players and is used with DVD-Video Discs (i.e. movies). Currently, the motion picture industry has divided the world into different regional "zones." These regions or "zones" correlate to the regional markets into which the motion picture industry releases movies. Simply put, RPC Codes are placed on Movie Discs marketed throughout the world based on the region of the world where they are being sold. These RPC codes help to control and prevent the pirating of new release movies into other motion picture market regions prior to their true release dates within those markets. The CD-RW/DVD-ROM drive supports the current RPC phase 2 industry specifications. The drive's regional code is set to the code found on the first DVD video disc that you load into your drive. The regional code will change if another DVD video disc from another region is inserted. Your CD-RW/DVD-ROM allows the regional code to change four times. The fifth time a different regional coded DVD is inserted, your drive will be permanently set to that regional code.