Many street and candid photographers use a similar style as you have described; I've been shooting street candids that way for over 40 years, but with a (D)SLR and a wide angle lens set to hyperfocus.
The best kind of camera for this work has an articulating viewfiender. That allows the camera to be operated discretely at waist level where the up-facing viewfinder makes composition much more precise.
Since the subject must be centered (or on an auto-focus point), poorly composed grab shots with a P&S on autofocus will likely be OOF since there is usually more distant background than there is up-close subject matter. The net result is that - unless precisely composed - the autofocus is likely to register on the background, and your intended foreground subject will be out of focus.
A camera with manual focus, wide angle lens, and an adjustable iris should allow hyperfocus: By stopping way down, and manual focus set to the sweet spot, the DOF is increased to the point that most normal subject matter will be in focus. This is a preferred technique for candid shooting.
Both the S90 and S95 have manual focus, manual aperture control, and wide angle capability at the bottom of the zoom range, but neither has an articulating viewfinder. For that you need to look at the G's.