Re: why the major price difference?
the points you give are good. with that said, if you look at a lot of other industries, the reason that online prices are so much lower is because the online vendors buy a greater volume of product thus bringing the price per piece down, most smaller shops can't afford to keep that sort of stock because it won't sell quick enough. Shipping should not have any sort of effect on the price of the product itself. if the shipping needs to be inflated, then do that on the shipping costs. Boxes and packing supplies cost almost nothing, for a while I worked for a shipping department and a single box is maybe a dollar, two if it's a huge one...and packing peanuts are also very very inexpensive.
the point you bring up with the costs of a website is moot because look at the price of a website and what it costs to run it and the cart services, and then compare that the overhead of a B&M store, and the fees they deal with in terms of card services.