Suspect they turned up with a caption generator (or if it was going through a TVC gallery the CG there) that didn't have the 2010 BBC copyright strap loaded on it - and the bbc.co.uk/commissioning site hasn't had the new line uploaded to it yet. (The 2009 strap is the last one I can find...)
(Or nobody wanted to try and work out MMX was the date in Roman numerals...)
I doubt it was a specific copyright issue - more a cockup.
It was because the BBC don't hold the copyright on New Year Live, nor any production company. The OB was produced by BBC Events and covered as 'news coverage'. The main firework event was a Mayor of London Event and was also broadcast on the official Mayoral website, but without the BBC interviews.
GM
nodnirG kraM
In instances where the the BBC doesn't hold copyright, for example The Queen's Christmas Broadcast, generally just BBC MMX would be shown. Particularly useful for morons such as myself who tune in solely to see the new numerals on the caption. Doubly particularly useful for super morons such as myself who are still reeling from 2007-2008 New Year's Eve being broadcast in Arabic numerals.