The button it replaced is a physical one, as it it's not an electronic switch to something, it just physically blocks the throttle from moving. If they implemented this in the game you'd have to click and hold the button, while moving the throttle, which would make it more difficult for certain set-ups.
Considering start-up is a once-per-flight kinda thing (assuming all goes well ¬.¬), it doesn't bother me that much. As long as it flies correctly and weapon employment is fun, though I'm still a bit confused with what liberties they took with that, but as I said, as long as it's fun. I'm more interested in troop transport than gunship to be quite honest.
