Lack of 32-bit Server platform
The biggest objection I've heard from customers to why 2k3 is still in production is that it's their mainstay for their 32-bit LOB applications. 2008 RTM really isn't an option (because it's terrible) and Microsoft decided to kill 32-bit from 2008 R2 onwards. They've not addressed this adequately in their intervening years of mucking around with Metro, and instead have created an insurmountable upgrade point. Projects like Drawbridge held promise for solving this problem- but the earliest we are likely to see any of the results of it are next year- and I doubt very much it will the hammer to crack this nut.
Domain joined 2003 is totally insecure as of the turn of this year. Very nasty exploit for AD joined machines found (that ran the entire Windows line)- and only 2008 or above got the fix. Profits put before customers by Redmond again means they'll have diminishing customer numbers with every cycle.
Biting the hand that feeds IT
