That is very true.  I work in the consumer packaged goods (CPG) industry and Wal-Mart is well-known as a big bully.  They have turned around the whole supply chain.  Used to be that a manufacturer would make something and try to sell it to stores.  A deal would be struck that would be advantageous to both sides.  Now, Wal-Mart dictates what manufacturers will make and at what price they will buy it.

Historically, retailers were never that powerful, and it was the manufacturers who were bigger and more of an expert in their area, so they came with recommendations of what they thought would sell well at the retailer.  Wal-Mart has become so big for its britches, and that is why the tables are now turned.  This leaves smaller retailers in a very vulnerable position, as they can't swing their fists in the same way. 

In addition, in 2003, Wal-Mart stopped sharing its sales information (information about what sells at their stores, taken when a product is run over the scanner at checkout) with anyone on a syndicated basis (meaning any manufacturer can have access via companies that provide this service--namely IRI and ACNielsen--I used to work for IRI).   They do share their information with selected Category Leads (i.e., the manufacturer who is the leader for the category, such as Procter & Gamble) via a tool called Retail Link.  However, this information is highly guarded with many stipulations and restrictions.  This puts smaller retailers in an even weaker position, as they cannot see what succeeds at Wal-Mart, and Category Leads are prohibited from sharing this information with other retailers.

There is ONE way that retailers can see SOME information on Wal-Mart, however, via a type of data called Panel data.  This is data taken directly from consumers, and distributed also via ACNielsen and IRI.  However, it's not "scanner" data and doesn't have the pinpoint accuracy or depth, but it IS something.