As far as I know (and someone please correct me if I'm wrong):
The most important factor is the performance of the engine -- not just in terms of power, but in terms of how it's meant to be used.
Modern German engines, especially BMW engines, are designed to have low internal friction so that they rev freely and can be used for a long time at high output. Some aspects of this design, like the special piston rings they use, can lead to higher oil consumption.
Many Japanese engines are usually designed for milder use, so they can be designed for lower oil consumption.
However, it's interesting to note that some Japanese engines are designed for performance, similar to the German engines. Accordingly, they often have higher oil consumption. A good example is the modern generation of Nissan's VQ series.