Well, they shouldn't. I expect far more from someone calling themselves a "designer" than their ability to draw a nice button or pick decent fonts. I expect them to be thinking about interaction, flow, "how it works", and so on.* If not, then they're qualified not as a "graphic designer", but as a "bad designer". If someone only wants to draw, they can call themselves a "graphic designer" and I'll call them when I just need a graphic (i.e. never, since I don't work in print).

* I expect the same from anyone who has anything to do with a UI/UX.