In my opinion, most native speakers use the two forms interchangeably. I don't find much support for the distinctions you suggest. Only context could make those things clear.
Hi, A: I bought a watch for him. If you want to get fancy, you could consider a meaning like this. A wants to buy a watch and give it to B. A can't go to the store to buy it, so he asks me to go to the store to buy it o