It sounds desperate but I'm sure not all miners will do the same. For some, if the price is too low, they would rather not sell at a loss and wait for price to go up again before making the next move.
The OP is correct in assuming that the miners are adding to the supply of bitcoin as they most likely will need to sell a good portion of their bitcoin to cover their electric costs however this fact is not what is causing the price of bitcoin to decline as much as it has been.
As the bitcoin economy becomes more mature more people will want to buy additional bitcoin in order to participate in commerce which will offset the effect of the miners selling their mined bitcoin