Where the hell are all these 50% off bikes? I'm sure as hell not seeing them in any LBS I've ever been to. I don't have the experience of BDop or others, but I've worked around the fringes of the bike industry a little bit, and I can confirm that the margins for massive sales simply aren't there. The massive "sales" of distributor/retailers like PB and Nashbar (and BikesDirect.com) are just a bit suspicious: they get to set their own MSRP on stuff under their label, which means they can claim that their aluminum bike frame (for example) is $399, even if they never intend to sell it at that price. But your LBS can't do that. You can only get away with selling over MSRP if demand for the product is very high; that's not typically the situation with bikes!

Anyway, there are differences between brands/makes of bikes, but it's a matter of geometry details and spec for price point rather than quality, for the most part. And, of course, color and logos.