What role does a stoneware bowl play in the baking of Artisan bread?

I don't see any reason to buy anything like that. It is correct though that steam is key to great crust!

You can simply use a spray bottle with water.

What I do, is preheat a flatish sheet in the oven at as high the oven goes (I usually go for 275 degrees C), on the bottom rack. Put the loaf on the pan, and mist the sides of the oven and quickly close the oven door. It's important that you don't have the oven fans on at this point (convection oven).

Reapply mist to the sides of the oven to create steam every 3 minutes or so for 15 minutes, or until you see a firm, nice crust forming. At that point, lower heat to 200 or so, and LET ALL STEAM ESCAPE. I set my oven to use it's fans at this point. Bake until finished (about 40 minutes more when I do my bread).

The reason I put it on the bottom rack is because the pan seals in moisture to the bottom of the loaf, or something like that. Atleast I get better results if I heat the bottom more.

Edit:

Of course, a preheated pizza stone is even better than the pan idea! I just don't have a pizza stone. Go ahead and use that, and you won't be disappointed. You could probably just set it in the middle of the oven, since the preheating will make the stone retain alot of heat.

You can indeed do what you ask - baking on the pizza stone with a steam pan. It works better to pour hot water directly in the pan when you put the bread in though, rather than just leaving water in the pan. You get a burst of steam and then a consistent small amount. It's a method that Peter Reinhart advocates.

The other common option - especially with high hydration doughs - is to bake it in a covered dutch oven for the first half. This approximates some of the effect of the earthen/stoneware. The steam from the bread itself keeps the environment moist.

You certainly don't need those pots for fantastic bread.

Tonights loaf - no earthenware ;) (I rushed it for dinner, so the crumb isn't what it could be.)

Baking on a sheet rather than a pan certainly gives more top-crust. A lovely dusting of flour on top for thick chewy crust is one traditional option where addition of steam is not ideal -creates plaster!

A nicely oiled metal pan can create a lovely crispy side-crust esp. after rolling dough in seeds or oats etc.

A shiny crust is achieved by a brief fine spraying immediately after baking (not for floured loaves).

The thickest chewiest country sourdough loaves I know are 'Doppelback', double baked, meaning baked longer and slower but never literally double unless you want caramelized pumpernickel...