You definitely get ease of adjustment. Look at any company's line and at the low end you'll see simple straps with simple fasteners to go along with simple shapes and simple graphics. As you go up you'll see fancier adjustments for both the straps and the headband and in general those fancier adjustments do help customize the fit (including ease of adjustment while riding) and allow for varying thicknesses of head coverings under the helmet. The fact that the vent designs and graphics get fancier as well with increased cost just makes sense from a marketing point of view. The cost-benefit curve is pretty steep though and you don't have to go very far up in cost to get most of the features.

And if people are willing to pay $200 for a helmet, why shouldn't they have that choice? Jeez I know women who spend way more than that on a flimsy pair of shoes.