I don't think one needs impeccable knowledge of anatomy to be able to tell if something looks off. You might not be able to pinpoint WHY it looks wrong but you'd still be able to tell that it DOES look wrong.^^
I often find incorrect anatomy to be extremely distracting. A piece of art can have perfect lines and flawless coloring/shading, but if the character looks like they have a couple broken bones, I just can't stand to look at it. All I think is "Ow." and "Why."
I'd also vote for a mixture of these two options... XD Then again I think no real person's anatomy is 'perfect' (different-sized feet or breasts, for example), so sometimes an 'inaccuracy' could reflect that... not just lack of knowledge or skill about anatomy. But if it's plain-out obvious the 'inaccuracy' in the picture is due to lack of knowledge or skill, then ... it can be a little bothersome. As someone who doesn't really know much about anatomy, I often miss these sort of things, but lots of my drawing-friends will notice and get bloody mad too... (Anatomy is one reason why I stopped drawing, lel.)