Question on capacitor voltage droppers in small power supplies

[cravenhaven]

I have just been repairing a couple of small 'embedded' power supplies that use a capacitor as the primary voltage dropper before rectifying and regulation. I notice that they commonly consist of a capacitor of about 0.5uf in series with a 2W resistor of 100+ohms and a diode and zener. What is the purpose of the resistor, why not just rely on the capacitor?. By my calculations the capacitor has an impedance of around 3-4Kohms @ 50Hz so what value does another 100 or so ohms add ?.
ie:

[HackedFridgeMagnet]

Limit inrush current.
Transients.