I agree that comic book physics don’t work in the real world, but the physics in the movies should at least be consistent with the internal logic in them. The first movie made it very clear that the kind of things the suit does are made possible by a source of enormous power (the kind of power that can propel the suit or its components at several thousand miles per hour for hundreds or even thousands of miles), namely, the arc reactor. This was made explicit when Stane was unable to make his big suit work without Stark’s reactor. It simply doesn’t fit with what was previously established that “battery power” (what kind of battery? Some super duper Stark battery that's able to match the power output of an arc reactor? Doesn't that essentially make it an arc reactor? After all, neither can produce energy from "nothing".) can accomplish essentially the same thing as the arc reactor (the boot jets work as well as the repulsor rays without being connected to the reactor). That's why I said it sure seems like the pieces have their own arc reactors.