I read that same article that Sagacity read (or at least one that was similar) HOWEVER, i read another article that disputed the article. It basically said thats the article is half right. A lot of the older style HID's had to be projected through a projector but many companies have developed methods to use an HID without a projector. It uses the same idea as many halogen bulbs. They put a shield in front of the bulb to reflect all the light to the back of the headlight housing. HID's dont reflect any different then a standard halogen. There are many cars out there that dont come with HID's standard (i.e. Prius, Lexus and Toyota SUV's, Escalade, Mercedes, Acuras, Mini Coooper, etc.) They do NORMALLY use only one headlight housing design whether its HID or not. Idk if any of this makes sense, its getting late.
I thought motorcycle riders are concerned about being seen... HID's are perfect for that.
-Sean