Then Graphic Design is product design as well. Posters, business cards, logos, books all need to go through a printing (or other) process to get applied to pap

Then Graphic Design is product design as well. Posters, business cards, logos, books all need to go through a printing (or other) process to get applied to paper (or another surface). And you get the best results when you know a bit about the printing process, how paper absorbs ink, the effect of varnishes, etc. That doesn't mean you need to do your own printing. Graphic design is also experience design. That poster is going to hang on some wall, complement the context, and catch the attention of people passing by. Then when people are drawn in, it needs to communicate clearly. So not sure why web design is different in this respect.