Re: would that really make any difference?
That's a very arrogant way of seeing things.
One point to squat all of those. The list of new unknown vulnerabilities that will never get patched because XP isn't supported anymore? NHS is a big risk knowing how much data there is in every NHS Trust system and it being publically in the spot light for not progressing to a supported OS version. Not just that, but a leverage system to push attacks on other systems used on wards etc.
At the end of the day, the NHS should not have computer systems sitting on an OS that is 13 years old. End of. If you were in a big private sector business (finance etc); you'd be in the firing line for being that slow.