You mean P = I * E? If so yes. And since E = I * R, P = E^2 / R. If the capacitors run at 170V, a 100 ohm resistor would have to dissipate 170^2 / 100 = 225 watts. With 100Ks that would be more like 0.225 watts, which is about right for a 1/2W resistor.
It's very unusual to run diodes in parallel like in the schematic for no good reason. But if you think about it, you can easily add a switch to this circuit to make it run on 220V by disconnecting your green line from between the capacitors and feeding it into the bridge. Naturally you'd disconnect the red line from the side of the bridge you attached the green line to. At that the resistors balance the voltage across the capacitors so they split the rectified 220v evenly.