Ok. Looks like this upgrade is not optional which is fair enough. Interesting to see if it lasts as long. Shame as I was planning on reusing the spokes this time. Last 3 rebuilds I've always bought new ones. Still on the original hub.
By the way I replaced the chainwheel/crank unit a couple of months ago. I asked about the new spider+chainring I could see on the new bikes but it seems that not all models use them. Is this true or was I looking at old stock? Logically it should be cheaper to replace the ring - and I can move it round to even out wear. The original chainring was completely out of shape. I estimate I should be replacing it every 12 to 18 months.