Not necessarily. When making reservations using Marriott's online tool, I have seen it show me a points stay reservation with a rate code stating that I will be required to either order an upgrade award(s) or pay XXX amount for the room. So it is possible to reserve a "higher" level room (i.e. better view, more room, C-level, etc.) using the online tool. Then you would only need to settle up with the hotel when you arrived. I have seen these fairly often when making points based reservations for beach-front properties where they have view-room upgrades.