It constantly amazes me how people put down a decision they don't like (or - not nessesarily in your case but I have seen it several times - can't understand) to incompetance, stupidity or laziness instead of the idea that the artist is making a consistant and conscious design choice. If WoTC artists are like
every other artist I've ever known, they have dozens of reference books on how pretty much everything looks - including anatomy and weapons and such.
Here's the secret to art, in a nutshell: 'Cool' surpasses 'Reality'. Once you have the rules down pat, then you also know how to break them in effective ways for effect or to convey a particular message. 'Style' surpasses a text-book correct engineering illustration, because the style
says things about the subject.
Yes, you could make technically correct weapons and armor illustrations. And all characters would wind up looking almost alike; more like soldiers than heroic fantasy characters. This is the death of any sort of illustration, especially one meant to make you go 'ooooooh, I want my PC to look
that cool'. Unless you're illustrating a Sears catalog or an engineering textbook, making something technically correct is generally not the way to go.
For instance in the
first Pathfinder cover illo, the goblins have these wicked serrated blades called dog-slicers. Yeah, it's simpler to make a blade that is a narrow triangle; they'd probably be more effective as well. it's techically correct. It's also boring as hell and says nothing about the goblins. Ok, did you get that? The blade design isn't meant to say a damn thing about the blade, but it says volumes
about the creatures who made them.
That is art. This notion also applies to films, books, etc.