When you experienced Ld-ers RC during waking life, are you doing it moreso:
To make it a habit that carries over when you dream?
To check and make sure that you are actually present in the waking world?
Does anyone REALLY question if you are dreaming when you are awake? And if so, isn’t that a little concerning? 
RCing is a mixture of both. I don’t think it’s concerning. The point of questioning if you are dreaming when you are awake is to carry the question over into the dream world. If you don’t ask the question, you won’t actually put together the idea of RCing with the idea of being awake or asleep. RCs are much more affective if you remember that they are a means of showing whether you are present in the waking world or not. I feel like you should always be sure to question if you are dreaming when you RC.
While I agree with you that a normal people won’t REALLY question if he is dreaming when he is awake, he won’t question that either in a dream, so we need some sort of habit , something test that we know if it is “positive”, we are dreaming. So you can say that RCing irl is useless in that we will never make the test work but it is the preparation needed for us to RC in dreams as well