That could be a bit of an apples to oranges comparison. From what I've seen the migration time for large corporate XP deployments has little to do with the OS

That could be a bit of an apples to oranges comparison. From what I've seen the migration time for large corporate XP deployments has little to do with the OS upgrade itself and everything to do with the application support issues. I was at a meeting recently where people were still saying that they had applications which would only run on XP, which was why they hadn't upgraded. The problem for corporates now is likely that they won't/can't complete an upgrade before the deadline and the risks of having unsupported XP are unknown. One theory is that a lot of potential attacker will be holding any XP exploits they have at the moment with the intent to use them after the end of support, when there will likely be no patch.