Robert_Charlton - 3:15 am on Mar 15, 2013 (gmt 0)
I was too quick to specify backlinks. Yes, Panda 1 would have more to do with it, and that would be about content.
I'm wishing you had a more precise handle on when this particular search result started popping up. As it is, I'd relate it to what was discussed in this thread...
Host Crowding vs Brand Authority
Over time, I've seen this "brand authority" effect shift more toward long tail and infrequently-searched queries. As I've mentioned elsewhere, it appears that as Google is getting enough data on the early pages to make granular choices for common queries, it's making adjustments. I'm seeing same-domain results now more for deeper pages in the serps and for uncommon queries.
This I take to be Google's linear ordering in multiple results pages of how it's regarding the likelihood that a searcher who is searching for your domain would be satisfied with your domain as opposed to the big brand site "widgets.tld". It's a statistical choice... similar to Universal results, eg... where Google needs to bring into one sequence different types of results.
PS: I should probably add that in terms of display choices as we're discussing here, weak linking and Panda are likely to be statistically equivalent. They are results that Google simply feels aren't as likely to provide searcher satisfaction.
What are you doing to fix your site?