Regarding the brass clips - I've been told those at hardware stores have springs made of zinc - which corrode and break in a matter of a few dives esp. if you clip and unclip a lot. Most diveshops that know the difference stock DiveRite clips, which I'm told have stainless steel springs, hence the higher price.
Ultimately the LDS is smaller (like a mom and pop store) and sees less business than a typical hardware store (many of which are turning into giant chainstores such as Home Depot, Farm and Fleet, Ace Hadware chains etc) which have massive economies of scale when it comes to purchasing power. So I'm not surprised about the price differences. I only buy regs (life support and annual service advantages with LDS), wetsuit (fit is important) and tanks (high shipping costs if purchased online) from my LDS, and buy everything else online, unless there's a big sale at the LDS.