One of the airlines I work with calls V1 5 kts early. After discussion their reasoning was thus:
The Captain is responsible for deciding.
He is prompted to decide by the call of "V1" to which he responds with "Taking off".
The call "Taking off" is a comitment to go.
If an engine fails at the same time as the co-pilot is saying "V1" the captain could still stop and he will have initiated the first action below the actual V1 speed.
If the engine failure occurs while he is saying "Taking off" the actual speed will already be at or very close to V1 and he will continue the take-off.
Note that the language this company uses is not English and therfore the call "taking off" is much shorter that the english translation.
So the concept is to limit the action to V1 by having the captain decalre"taking off" at V1.
I have no opinion either way
