You're right... I just went and looked it up. You earn points on your room and up to 2 others. It does sound like you won't get night credit though.
Here from the T&C:

"member is eligible to receive points for staying at participating Marriott Rewards hotels for his/her guestroom and up to two additional rooms. All rooms must be reserved and registered in the member's name and the member must make arrangements for payment of all rooms on a consolidated bill, which should be requested at time of hotel check-in."