I know with Matt he's there for three years minimum

nope. i'm pretty sure he's got a contract that specifies one year for certain, which can be renewed for one or two further years (i forget which) after the first year is up. dunno if that's so the beeb can replace him if he's not popular enough or if it's so he can renegotiate for a higher salary if he ends up being very popular. (or mebbe both).