Brand xyz product Jimmy
So it sounds perhaps like the branding/named entity effect has been turned up to include leading vendors in addition to manufacturers.
In this previous discussion, from Aug 23, we noted that Google treated a branded query in part like a site search, returning more results from the manufacturer's domain.... Google To Show More Results From a Domain http://www.webmasterworld.com/google/4191279.htm
A search for [apple ipod], eg, for those tuning in late, returns seven results from the Apple domain (and subdomains) of that domain, with the last three results then coming from Wikipedia, Amazon, and cnet.
To some extent, I've noted that the number of branded results depends on how strong the branding effect is with that site, and undoubtedly the size of the site and the number of pages it has fitting that query.
I still haven't seen exactly the type of serps you're describing. I have seen something perhaps similar, where if I search for...
...in some areas I'll get three results from one domain, then three results from another, and then two or three from another, etc... where all of the domains are leading vendors, and the productname is a generic unbranded product.
Any other observations along any of these lines?