Well, since noone else is I will take a crack at this question.
Bear in mind, I am just a content engineer, so I don't deal directly with Stardock and can only comment about what happens at GPG.
Stardock sends us a list of changes they would like to have done. Those changes are handed out to the appropriate people. When those changes ( or at least a bulk of them) are completed, a build is made and sent to Stardock as a WIP build to have Stardock QA take a look at it.
If any bugs or issues are found they contact us back to have further changes/fixes made. It goes back and forth until Stardock QA approves the build.
As for the Stardock QA process or how they decide what goes into each patch, I have no idea.
Hope this at least helps a little.