I think that the punishments you are referring to are more of the roleplay type and only meant as such.
Instead of a Dominant saying, you were a bad girl, now lets do something you enjoy for being such a naughty slut, he or she uses that typical form of I am going to punish you now for your insolent behaviour, even though I told you to do it anyway.
It's not really a punishment, but more to set the tone to get both parties in tune with things.

A punishment, is not intended to be memorable or enjoyable, it's going to be something you dislike. If a Dominant uses punishments in that aspect that you state, he is not correcting the behaviour very well.

I have been punished in such a fashion, but he was testing my limits and seeing how far I would go with what was asked of me.
If I was given a task I couldn't do, I was "punished" with another task which was just as difficult.
I knew I wasn't really being punished, it wouldn't be really wise of him to punish me with something I couldn't do either.
He was testing limits, seeing how I would react and how far I would go with each task. It made finding my limits more enjoyable.

I have been punished once, and it was a punishment that was effective, and something I definately did not like.
It wasnt' something I enjoyed such as a spanking or some other form of play, it was geared to not be enjoyable on my part.

Punishments can be used as a form of play or when they are warranted are used to correct unacceptable behaviours.
I would think that when you are punished you will know it.