^No-one has actually said that they don't think any of these actors will or won't return. We simply don't think it's a fact
that they will return.
No-one can be so certain about something which is dependent on so many factors - story, salary, timing, availability, willingness, size of their role, etc.
Yes, I personally think it's likely
that Tennant and McGann will return, I think it's unlikely
that Eccleston will be in it and I think it's possible
that the surviving Doctors from the original show (Tom, Peter, Colin and David) will make an appearance. But believing so, even if it's based on firm evidence, is a long way away from knowing so as a fact.