I should probably clear this up - we (Frozenbyte) have always owned our games, but indeed Shadowgrounds was distributed in North America by Meridian4 (and on Steam as well originally, we reverted the rights in 2010 or so when the contract expired, although I always say that Meridian4 is one of the few "publishers" [they're a bit small to really use that moniker] who were always good to work with, even during tough business discussions), and Trine was distributed on PSN by Nobilis and in PC retail in several countries by Nobilis (and through a sublicense by SouthPeak in the US - oh how we wish that had never happened). Trine we self-published on Steam all along. Trine 2 we licensed for XBLA and PSN to Atlus, PC retail in Europe to Focus Home Interactive (who are great) and kept other distribution rights to ourselves. We are self-publishing the Wii U version in the Nintendo eShop.
I would imagine some of the other games mentioned in the original post have similar distribution licensing agreement things going on, certainly when it comes to XBLA and PSN at least (it was and still is a bit tough to self-publish on those, technically possible on PSN but in many cases not an option if you want to release on other platforms too, although the situation may have changed recently).
- Joel, Frozenbyte team