They had to throw a bone to the 12 year old customers... I still consider the making of a major FPS title in a hundred year old setting, to be a bold move. It would be so much easier and safe to be unrestrained by any historical limits, and go for an alien attack future. All sorts of colorful orbs and rays are flying around, people and aliens are flying around, huge robots with legs are flying around too - everyone is fucking happy.
Even if they plague the game with "experimental tesla-guns", especially probable with later expansions, one can count on some minor degree of taste when it has to fit in the rest of the game.