The 1/1500 s shutter speed is pretty fast. Look what you can do with it: see left image in
Digital Camera (post #11)
Faster shutter requires more light or sensitivity (both cameras have ISO400 max), so faster than 1/1500 s can be used only in very bright sunshine. If there's not enough light, you could use bigger apperture, which reduces the clarity of the image.
The interesting thing with Powershot is the longest shutter speed, 15 s (instead of Casio's 4 s), so it's more suitable to take pictures of a static object in low light, or making some interesting effects (e.g. car light trails at night).