Light/Switch definition

[gbuico]

Hi all. I might be missing something of Domoticz overall design but I fel very confused.
Let me simplify with an example. My Raspberry has a Piface Digital 2 directly cnnected.
Not very important what this hardware is but it has 8 digital input and eigth digital output.
When I acquire them in Domoticz they all appear as Lighting 1 and Impuls (exactly what the Wiki says).
Now, I define some of the inputs as "Blind Inverted" and some outputs as "On/Off" and again evrything is ok.
My problem is... does it make no difference to Domoticz whether a device is input or output?
Why do I have the possibility to click on a device defined as a Blind and receive a message back saying "Error sending switch command..." when is well known that you cannot send a command to an input?
More... my outputs are relay, defined "On/Off" but this definition may apply also to a wall switch or whatever other input device
Why does Domoticz seem to deal with inputs and outputs the same way?
If someone has this clear can please spend two words to clarify?
Thanks