I could be wrong, but I think the A440 confusion is due to the language of the original post. When he said:
and retune it in A440. [...] the tune of C key starts always in Ab.
he was referring to transposing the keyboard, not tuning the keyboard. Those are two different things.
Transposing the keyboard, which is common among a certain type of keyboards, will move the keyboard up or down half steps. The reason for this is that you've learned a piece in E major, but the trumpet player wants to play it in D major. So you can just transpose the keyboard two half steps. It sounds like it's in D major, but your fingers are still in E major. (It's also essential when accompanying vocalists who have to work with the limitation so their voice.)
Tuning a keyboard moves every note on the keyboard up or down a small fraction of a half step. This is designed so that the keyboard will be in tune with the other instruments in the band, and is meaningless if you're playing with yourself.
The modern standard is that the A above middle C vibrates at 440 cycles per second (or Hertz). But not all orchestras tune to that standard. In the baroque period, there was no standard. That's tuning, and from what the original poster said, that's not the issue he had at all. His problem was that the keyboard booted up in a transposed position, and he wanted it untransposed when he turned it on.
Most modern keyboards are relatively easy to transpose, with either a dedicated button or a single menu step to the transpose control. Most modern keyboards are harder to tune, with the tune command buried somewhere deep in the system settings. That's because you might want to transpose each song differently, but will generally only change the tuning at the beginning of the gig, and even then it's rare.