They might be trying to encapsulate things so that they are sure threads get stopped when the objects go out of scope.

But, I would probably do that by having a class that contains both the thread and the data that the thread needs to access. Then its destructor could first join the thread and then clean up the data. For example, instead of a WorkerThread that contains a vector of WorkItem, have a BackgroundWorker that contains a Thread and a vector of WorkItem.