Why is F6.3 the max? (DMC ZS7)
2. more important, beyond f/5.6 (or even f/4) these cameras lose a lot of sharpness to diffraction (scattering of photons as they go through the tiny aperture, forming "Airy discs"). The image would be really mushy and soft at f/16 on small sensors... not useable, probably.
To put this in perspective, by ƒ/6.3 you're not capturing much more than 2 Mpixels of detail. Actually, this particular camera has a hard time ever capturing 12 Mpixels worth of detail: at ƒ/3.3 the most you can realistically capture on a 1/2.33" camera is about 10 Mpixels.