Skeuomorphism is when you ease the adaption of a product by using a similar user experience as the older version. An example, the early iPhone icons looked very realistic and only became more abstract as people got used to the interface.
I was thinking that this is a necessary technique for introducing any new version. There should be a bridge between old and new, a way for users to easily create an analogy for themselves. Too big a jump and they won't try it out.