Having worked at for a couple of NHS Trusts before, I can also confirm that XP and IE 6/7(and at a push 8) are still very much in use; the NHS as a whole is certainly one of the largest employers in the UK.
This may be very true but a website creator has to be pragmatic and decide "Am I dealing with NHS or what is the chance that NHS staff would be interested in my website" If the answer is zilt then clearly he has to move on and cater for the customers who are likely to bring in some do$h.
People in South Korea are still using IE6 (about 86% last time I saw the IE6 count-down figures) but that does not mean I should continue supporting IE6 because I don't have customers in South Korea.
IE8 is a different matter because XP is still being used widely and some companies are not willing to use Mozilla products because of its open architecture. They think hackers can exploit it easily though I can't live without FF.