The mere presence of voltage does not create an arc, current must flow as well. A coffee maker uses some tens of watts making the current too small for anything really to happen. An iron is another story as others have pointed out. The heater element in there could be slightly inductive as well, causing an additional kick but even so, the current should easily be enough to create a spark (not an arc really, that is something different). Whether you get a spark or not depends on if the thermostat is closed at the moment you pull the plug and, what exactly happens to be the phase angle of the line voltage at the instant of disconnection. At zero crossing (of either voltage or current if the load is inductive) you get nothing. And anyway whatever spark there is, will be extinguished at the next zero crossing.
So don't worry about it, it is not a problem. Just an interesting electrical phenomenon.