Because they are projectors, not HID lamps. BMW (for the Xenon question) uses a bi-Xenon HID system on the newer models....meaning the HID lamp has a filter to act as a Hi/lo beam. Projector lamps are simple an improved design to disperse light from standard bulbs. A perfect example is the mid-late 90's Acura Integra headlights.

__________________

An unwavering defender of those I see worth protecting.

"promote the general welfare, not provide the general welfare"

We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.