Big organizations in general, government or corporate, are terrible at managing software and updating regularly. This said, a special mention should go to Microsoft, for making it so "simple" to upgrade...
On Wednesday, ComputerWeekly reported that the UK government agreed to pay Microsoft £5.548 million (approximately $9.1 million) for continued support of Windows XP, Office 2003, and Exchange 2003 for all British public sector customers.
via Not dead yet: Dutch, British governments pay to keep Windows XP alive | Ars Technica.