I think I'd see this from another angle than most. I'd rather be given a list (especially if it was not even directed at me) to give me a better idea of what the kids actually like to play with.
You are allowed to decide whether to buy from it or not, but I know in my family we (along with everyone else) ask the parents what the kids are liking or what they need anyways. So a list just likely makes their life (and mine) easier instead of answering the same question many times to family/friends.
Many GP friends that I have get upset at the parents when their gcs are not wearing the outfit they bought them or have the toys out that they got them. Maybe they don't like them because they never asked! So yes, get the gifts you want to give gc, but have no expectation of what your gc or their parents do with them. My daughters mother in law acts like this to her. Gets extremely bothered when she is not made a huge fuss over gifts they never even asked for and is actually quite overwhelmed by toys taking over their house. It's a good problem to have I suppose considering the alternative, but this may be another reason for lists, to prevent unnecessary "stuff" everywhere, especially if it's something that can be very messy.