The thing that Lister believed was the reason Kryten was being replaced by Hudzen 10, the ultimate machine.
Further Explanation: the term is taken from automobile lingo, from when a car manufacturer would add some minor cosmetic enhanchment to a model of vehicle and consequentially say it was 'new and improved', though for all intents and purposes, it was unchanged. An example I have seen recently was Chrysler selling an 'executive' model of one of its cars, where the only difference from the 'regular' model was the addition of a metal-flake paint job.
This phrase can apply for most anything that is being sold as 'new and improved', when its improvements over older models if infintesimal in all real important respects.