Hi Nite:
You said: "I �m more interested in the living speaking language rather than the grammar, but I can �t help being curious and find out a, let �s say, grammatical explanation."
This caught my attention...
I inform my students that, for just one example, "Me and him" shouldn �t be used as a subject in speaking and writing, because using it makes them sound less intelligent than they are. I encourage them to understand why it �s used (see great explanations above), but to be careful about using it, because it can ruin their chances in a job or college interview--or another time when their quality of education really counts.
Keep up that healthy curiosity!
Your American friend