How does it make you feel to know that the manufacturers have created these sweetheart deals with the likes of Amazon, Walmart, Circuit City et al.. to sell and ship the hot products they no longer allow your distributors to sell to you? I thought transshipping was 'bad for business'. How do you B&Mers feel about it? Those friggin blue blood elitists are squeezin everybody - don't cha love it?
Further to Robino's answer which is spot on: it is volume. Anyone can negotiate 'special' deals if they can offer sufficient volume; it is simply easier for the biggies as they have marketshare, history, and credit. They also generally have to work with much tighter margins than I would ever accept.
Play the best you can in your own league. Plenty of profit and far fewer headaches in the niches.