A while back, Eurogamer ran a report revealing that full-resolution stereoscopic 3D using the HDMI 1.4 standard was coming to the Xbox 360. Five months on, Batman: Arkham City is the first shipping game to utilise it.
Previously there has been some confusion as to whether the Xbox 360 hardware is physically capable of carrying the HDMI 1.4 stereoscopic 3D signal. There was some concern that the older HDMI 1.2 standard supported by the Xbox 360 couldn't be extended in the same way that the HDMI 1.3 controller in the PlayStation 3 was repurposed to support the new standard.
MS should have had Gears3 feature this.