Motivation and Internal Drive

I'm not sure if this occurs more often with people with AD/HD or other learning disabilities, but in my experience those individuals are more motivated by external rewards and are less likely to be self-motivated. Since children who struggle need more encouragement and support, I wonder if they grow used to it and rely on it rather than find internal ways to motivate themselves. I've seen this in children who want to know up front what reward they will get for completing a task. They have become dependent on external reinforcement of some kind, either verbal praise or concrete rewards.
The mentality of "it's not my job" seems to go along with the difficulty in motivating oneself to do less-preferred activities. At my house, I often hear "It's not my assigned week to clean the kitchen." Even though the speaker is without clean dishes for his own meal, he cannot bring himself to do a job above and beyond what he is assigned and fails to see how the extra effort helps him and the rest of the family in the long run. You know the sense of responsibility is shallow when someone walks past a crumpled paper on the floor near the trash can because she didn't put it there and it's not her paper. These children don't share ownership enough to contribute and initiate outside of the specific requirements told to them by others.
When faced with a large task like cleaning her room, Beckie gives up before she even starts and concedes to living with clutter. She likes having a clean room, but can't make herself do what it takes to accomplish it. Only when threatened with consequences or offered an incentive can she force herself into action. She responds to the external prompts and can't seem to create the internal drive and motivation for herself.
I fear that externally motivated individuals will limit themselves to doing what others tell them to and will be disappointed when they don't perceive the external praises and rewards to be adequate for continued motivation.