Just remember that the gear is only locked for takeoff. I am not sure that in the end we have more margin for preventing a tail strike. Depends on how you look at it. For a given weight, I guess so but Boeing also just ups the max allowable weight for a given situation resulting, I assume, in the same margin under limiting conditions.
Subject to confirmation by someone in the know.
How does the aircraft know when to lock the gear? Just like it knows when there has been an engine failure and does certain things for the pilot automatically, it knows that it is taking off and locks the gear. Exact details on how? My only simple answer is... it is smart.