I thought it was believed that *they* were getting actors to play the First and Second Doctors? Granted I know it was just a rumor, but there's no reason to believe it couldn't be true, unless it's been shot down by someone in the know.
Sounds like a money issue if this is true. Instead of the BBC worrying about how much money one or more classic Doctors would want to be in the special, they get 2 actors to play 1 and 2 that can be paid at a much lower rate. Is the Wax dummy of Baker from the 5 doctors still available? I'm sure he wouldn't demand too much! LOL