Why ? It works, it's fast, it never crashes. So why ?
One thing is so...I sure as hell don't go with this "it's new therefore it must be better" philosophy that MS promotes.
You just don't get it do you ?
Come April 2014, Windows XP will be fully obsolete.
Microsoft will no longer issue patches for Windows XP.
You do not use an unpatched Windows operating system connected to the internet. End Of. Sure, if you're going to disconnect it permanently from the internet I don't give a damn .... but if you're going to use a computer on the internet, even if only intermittently, it needs to be patched.
And please, don't waste my time or yours trying to tell me "oh, I've got this firewall and this anti-virus" ... doesn't cut the mustard I'm afraid. Without a patched up core OS, anything you run on top of it is vulnerable. Fact.