This is all to do with dip beam patterns, something that it appears is required in European law but, it seems, not in the USA. The point being if you're going to order a Euro spec headlamp assembly then it will have a dip pattern and you need to make sure you get the right one.
Basically, in Europe when headlights dip they do not produce a flat cut off in front of you (a straight line across the road). They are designed to throw the light further along the verge (your side of the road) to light up the edge, illuminate any signs and highlight any obstacles. Hence, the lights should dip to the side of the road you drive on. If the pattern were the other way round then you would be throwing light into the oncoming traffic.
This by the way is all achieved through the reflector and lens design and has nothing to do with the bulb that's fitted. That is unless you have Xenon headlamps and then it is the shutter in the lamp that produces the pattern.
As the USA drives on the right it is important that you order continental european headlamp assemblies, dipping to the right, and not those for the UK where we drive on the correct side of the road
Hope that makes sense.