Olympus SP-570 UZ has a 10.0MP 1/2.3" (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Panasonic ZS40 has a 18.0MP 1/2.3" (6.17 x 4.55 mm ) sized CMOS sensor and features Venus Engine processor.
Panasonic ZS40's sensor provides 8MP more than Olympus SP-570 UZ's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the SP-570 UZ and ZS40 sensor size comparison.
Olympus SP-570 UZ and Panasonic ZS40 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.