Doc, as Ron pointed to, see 220.3(9)&(10)
In a residential circuit per the NEC, as many receptacles as you want, IMO this is by design to try to provide the typical homeowner as many receptacles as needed with out extension cords all over the house. Just because there may be 20 receptacles on a circuit does not mean there will be any more of a load than if there were 10.
Now, in other than a Delling the 180 va per yoke comes to play.
Some local codes did limit the numbers to lower amounts, but that would be specified on the exam.