Why doesn't he count - if McCann does then Cushing does.
Because it's not part of the continuing story, more like a film remake. McCann is the 8th doctor, as established by episodes since. The "Doctor Who" that Cushing plays has no real relation to the rest (his name for a start).
On the subject of Tom Baker, he's agreed to do a new audio adventure for the BBC having previously refused to. Apparently it was as a favour to Nicholas Courtney (Brigadier Lethbridge-Stewart), but he's too ill now so he's been replaced by Captian Mike Yeates. I hope it's not serious, would be nice for the brig to pop up in New Who. He's turned up in an episode of The Sarah Jane Adventures.