Define "major jewelers." Short answer making an assumption on what your definition of major jeweler is: besides not being an actual storefront like most of those jewelers, and having significantly less overhead to pay for buildings, tons of employees, huge marketing budgets, etc., if you're comparing their pricing to places like Tiffany or Cartier, or hell, even Kay's/etc, it's because you're not overpaying for a brand name, and you're not overpaying for "convenience" factor of walking in, seeing the name caché and assuming it's the best because of said name. Just because there's a fancy brand on it, does not make it the best there is. I go through scads of inventory for Tiffany, et all, and find very few legit contenders worth a real look in terms of well cut diamonds. They're playing the emotions, they're playing the convenience and they're marketing like crazy.
As for BGD, or High Performance Diamonds (the CBI brand is slightly higher but seriously incomparable to pretty much anyone out there esp in terms of consistency), or a few other online vendors like Good Old Gold, WhiteFlash, etc., you're buying a much higher quality product, with more testing done to confirm the quality, and not really paying for a huge marketing budget, for starts, so any money usually gets invested right back into the product to make sure it's maintained at that level.
