NutLoose - a MAYDAY doesn't quite guarantee radio silence as there will be other aircraft on frequency which the controller needs to keep apart until handed over to someone else. What it should do is stop other pilots initiating non-essential comms like requests for re-routing or weather updates. It also doesn't stop ATC talking to the distressed aircraft: the way to achieve that is for the pilot to transmit STANDBY (which is still only a temporary request).
I think MAYDAY and PAN-PAN serve a very useful purpose in an ATC environment in that they make it immediately obvious whether you are likely to comply with clearances. MAYDAY for those occasions when you do what you need to do and tell someone about it later; PAN-PAN when you can fly 'normally' if given priority. A MAYDAY should therefore get everyone else on frequency listening carefully to ensure their own safety and prepare for possible avoiding action. Achieving the same clarity with an IFE just takes more radio time.