Me neither but NPD are now so entrenched no competitor could establish itself. But what I meant was that in the US there is a market culture of competitors co-operating so they don't have to compete with each other. Competition is good for consumers but bad for companies who don't want to compete. Just look at the way utility providers magically focus on boundaries so there is little to no competition. Or the ludicrously small fines handed out to companies who breach regulations.
It depends on volume more than anything. The larger the retail store the more products they carry and the more manufacturers/publishers are involved. It's impractical even for large retailers to have a direct relationship with actual suppliers/publishers, except in high volume or high margin cases. Bear in mind many retailers carry hundreds/thousands/tens of thousands of product categories, taking just one - video games - they do not want to have people manage their relationship with EA, Activision, Ubisoft, Konami, Take Two, SEGA, Capcom, Telltale and the dozens of other publishers. Video games, like music and movies, will almost always go into big media distributors who deal with all the publishers, records labels and movie distributors, then supply great swathes of choice to retailers.
This doesn't impact retailers ability to include special DLC, they can secure rights to these separately and package them in before actual sale. Most of this will be done by the marketing firm, who often as not, are not the publisher.
I'm sure somebody on the board has a friend in retail. They will be able to confirm.