It is really not possible to take business away from high-end retailers by buying online, because the online seller is also a high-end retailer somewhere. I agree with Elizabeth on they should all be online in some respect.
There are also quite a few manufacturers that still prohibit online sales of their new gear. B&W Loudspeakers is one. Note the one dealer advertising new B&W on Audiogon states he will not risk losing his franchise, so you must visit the store to buy it. He also only quotes MSRP $$. He is probably also prohibited from offering a discount online even if you come pick it up at the store. B&W's especially the lower models sell like hotcakes and provide dealers with the cashflow needed to be able to sell the more exotic slow moving gear.
Even if you are buying used equipment, someone had to buy it new first; and you buying it used gives that person cash for more new equipment.