No IE6 won't be around forever, but if, in 2014, they can directly upgrade to IE10, say, then they will have avoided going IE6->IE8->IE10 and thus have saved the cost of an upgrade.
The problem is with this argument is that you can keep applying it forever. Also, a number of relatively smaller steps are easier to manage than one single big step.
A sensible step would be to get into the habit of upgrading browsers/tools. A workplace that finds it traumatic to upgrade to IE 7, 8 or 9 or from Windows XP or Windows 7 or even from Office 2003 to Office 2007 is not going to be prepared for changes in the future.
I think you're missing that some of those small steps weren't obvious at the time everyone was writing software that the government leans heavily on that only works on IE6, the people that developed it are probably long gone by now and rewriting everything is hardly justifiable.
Large banks are having a hard enough time ditching it and they have a clear motivation to do so to aid competitive edges.
Actually you can't (not in this case at least). Microsoft promised to support ie6 until april 2014, so they can't apply the argument after that. And ie6 -> ie8 (-> ie10) step is probably about as big as ie6 -> ie10.
Makes sense to me.