There's no reason not to increment the version number along with the revision number - This is a major update, after all. It'd be like... I don't know, marking the Xbox 360 Slim as just "Xbox 360" but having a higher number than the original one somewhere on the case. It deserves it's own title.
Well. They did call it Xbox 360 Slim, not Xbox 361.
This is the Shadows and Shaders update.
It's also software and not hardware.