Dear Linbin:
Many at first feel as you do. However, that is because research and papers are almost nonexistant on this subject as the researchers for the OGI are finding out. Their research is finding that the pelvic angle differences make a huge difference to their assessment and subsequent therapy.
Please do not too readily dismiss this idea. I feel that when the OGI has finishes the study and the paper is produced that the initial reaction will be like yours. However, as the test becomes more "mainline" that many will wonder how they did without it.
My suggestion is that you try it. You will have some problems integrating it at first. However, its value will be shown in short order.
Pelvic angles in the population with no back pain are near to the horizonatal plane. Those with low back to extremity pain deviate greatly.
Best regards,
Neuromuscular.