There are stories going around that only DVD-RAM will support these kinds of features, e.g. recording a movie while watching a delayed version of it.
I know this is rubbish technically (a hard disk is a far better/cheaper solution for random access storage like that) but I never put it past the makers to cripple products.
Anyway, I have decided to abandon the idea of a VHS+DVD recorder (like the one I gave the P/N for) and I will get a top end DVD-only unit, whose spec includes the features.