The sales tax issue is a big one for etail vs. retail - and you're right it can make a huge difference on a big ticket item. I've heard rumblings for several years on imposing sales tax for ecommerce but haven't seen it happen yet.
Etailers with a retail presence in any state where their online customers shop, are required to collect sales tax - places like Staples/Staples.com charge tax because they have stors here.
Following that thinking it's actually cheaper for people living farther away (out of state) to buy from etailers.