I thought I was pretty clear about distinguishing between graphics quality in general (texture resolution, draw distance, shadow complexity, etc.) and resolution specifically. If you look online, there are a lot of discussions about “Which is more important: resolution, framerate, or graphics quality?”, so clearly people think about resolution as something separate from graphics quality.
That's why I think that saying, "X doesn't do 1080p resolution" doesn't tell the whole story. I can take a low-end PC graphics card and get it to run at 1080p at 60fps (or even higher) by cranking all the settings down to the bare minimum. but that doesn't mean you would necessarily want to play that way. And as others have said, a lot of Xbox One games run at 900p instead of 1080p.