I don't think the Springtomize app is accurately displaying it. Mine showed ~70-100 MB with no apps running. I installed SBSettings just to see and it showed I had ~250-300 with in the same state
The springtomize "Time - Free RAM" status bar setting doesn't work on my 4S either. Hopefully it will be updated soon because I don't want to have to use SBS just for that one thing