"Tennant has been confirmed to star in the lead role for a number of BBC One specials next year. The fifth series, with Bafta-winning writer Steven Moffat at the helm, is scheduled to be broadcast on BBC One early the following year. Moffat is to take over from current writer and executive producer, Russell T Davies, from 2010.
It's the first line "Tennant has been confirmed to star in the lead role for a number of BBC One specials next year. "
"a number of BBC One specials" - so maybe not 'all' of them.
I don't think Tennant will be the Doctor when Steven Moffat starts weaving his magic at the beginning of Season 5.
I also agree with some of my friends that Steven Moffat should bring back one of his own creations as the Doctors Companion - Sally Sparrow.
Doctor Who Finale Watched by 9.4m (BBC Online; Sunday 6th July 2008)