Non-load bearing walls can be 24" oc.
Your idea would be cool, and you could have used 2" styro for insulation with good results. The only issue I would have with it is that if you ever want to change you layout you have a hole to fill. These built in scenarios are great at first but people usually like to change things up now and then and you really are commited when you build in.
I am about to help someone put a suite in their basement, we are trying to finalize a layout and determine where the kitchen will go, and one wall has a built in projection TV and stereo. It looks great but is dated, and even though you can still fit a nice flat panel in the void its wasted space and commits the space to only one layout.
Anyway, I still think your idea has validity, just throwing in my 2 cents.
