The "In-lens-system-is-better" myth was started and perpetuated by various publications by Canon including the most often quoted White Paper. The fact is that there has been no objective testing done comparing various system. One reason being that it is very hard to implement a image stabilization test while eliminating other variables.
Canon is worried about the SR/AS trend, so much so that they put out a full page ad in photo magazines advocating the in-lens supposedly "superiority" over in-body system. This would further perpetuate this myth with the mis-leading ads which was full or errors. In the ad, Canon stated that they chose in-lens method because they tested both and found in-lens system to be better. This, of course, cannot be true. They first used in-lens stabilization back in the film days because there was NO OTHER CHOICE! You can't possibly move the whole film around.