I'm thinking everyone's ideas are probably right on target. I have a lot more direct sunlight, more windows, and softer carpet. I never thought that the specific reasons I picked the place would delight them so much!
I'll see if I can get any photos of them. They're just so happy and bouncy now - Bouja jumped to the top of the fold-out closet doors the other night. And she's my mommy cat - reserved and quiet. I have a feeling that will change now!