That's not true according to the ATmega datasheet, in section 28 under Electrical Characteristics the absolute maximum rating for "DC Current per I/O Pin" is 40 mA. There is no distinction made for whether the I/O pin is being used for input or output. If the I/O pins were capabable of withstand appreciably higher input current than output current, that would be listed because this is a potentially useful difference.
You are failing to understand a basic tenent of Ohm's law. Only the load resistance determines the amount of current flow if assuming a fixed voltage (5vdc in this case). As an input pin has many meg ohms of input resistance (look up the value in the datasheet), how is it possible for any significant current to flow into or out of a input pin? It can't. Only if the external applied voltage exceeds +5.5vdc or under -.5vdc, where the input pin clamping protection diodes start to conduct, can any significant current flow.
Lefty