The longer answer is about the mismatch between PCs and mission critical enterprise computing. There is blame to spread around for that one.
Supporting people who run at 13 year old 32 bit desktop OS is a money losing proposition all the way around from Microsoft at this point, both in lost time and in lost sales of later version of windows.
The thing is that Microsoft's profits is what matters here. IT is their product.
As a developer, I actually loathe XP, simply because It's another platform I should test things on before I can consider it working. Generally, the users running it are doing so because of 2 things: lock in by a different vendor or a total lack of IT budget. Either of those things is just asking for trouble, So, when a client starts to ask about XP support I start to get worried about the bigger picture.
To put it another way, Would you want to write extra code and run extra tests to support windows 98 today? What about windows 95? 3.1?
I really don't.
True, but those people are needed to continue to support XP Embedded. So some of the work is being done...
Note: I'm not hankering after running XP, but I am realistic about the effect of the $200 per screen annual tax on mega-corp computers. That isn't going to win friends and influence decision makers lets just say.
http://www.theregister.co.uk/2013/06/19/nuke_plants_to_keep_...
These businesses had a decade to plan to transition off XP. It's not like other vendors that have no planned EOL dates and don't even announce their plans. Contrast Microsoft with Apple where Snow Leopard, which is only 5 years old, is suddenly abandoned and is no longer getting security patches, but there's been no announcement.