Selecting the frame and using the scale fields in the Control panel works here...
Object > Transform > Scale only transforms the box.
Object -> Transform -> Scale of 200% when applied to a text frame full of text works here: frame doubles in size, text doubles in font size. (CS5.5. and CS6 on Win7) It works on images, too.
In fact, I almost can't reproduce the behavior you report at all. The exception is this: If in CS5.5. I fill a frame with text, and then select the frame with the Direct Select tool (the white arrow) and use Object -> Transform -> Scale, then just the frame changes in size, and the text doesn't change. When you select the frame, which selection tool are you using?