That is also standard on the Underground, introduced on all new stocks since the Central line was upgraded with the 1992 stock.
It is by far the safest system, allowing the driver to observe the platform train interface as the train departs, and, where fitted, before the train arrives also. I'm surprised this system isn't mandated, or at least strongly recommended for the reason of the improved visibility it provides. I suppose the reason for the industry preferring on-train mounted equipment as opposed to platform mirrors/CCTV monitors, or this solution (track to train CCTV) is the fragmented nature of the rail industry, where presumably the maintenance of the platform equipment (cameras/mirrors/cabling) would be the responsibility of Network Rail, whereas the on-board equipment would be the responsibility of the Toc.