If you click on the user's name you will find some tabs, one of which is "About me" and there is a location for them to put in the software they work with. In the case of this artist:
Campaign Cartographer 3 (and its suite), The Gimp, Terraficta and Photoshop
Bogie does quite a few maps that look along these lines so you might check out his work as well. Bonus is he is quite active on the boards and might be able to share some of the details. He's not the only one who creates things along these lines but he's the one who came to mind at this moment. FYI, he uses DundJinni & Photoshop.

I'm pretty sure they use Photoshop for touch up work and creating the background then use the clipart from DundJinni to place the beds and stuff but at least you have a place to start.

Hope that helps.