lilmod, nowhere have you indicated that Rav Bodner advised you that the decisive factor in the psak was the survey. You appear to have come to that understanding (specifically the reason for the psak being the survey) from other sources. Various rabbonim have ruled to wash on pizza for various reasons. And Rav Bodner and Rav Forchsheimer may have ruled to wash because they believe that it is customarily only eaten in America as part of a meal. But that doesn’t mean they concluded that due to this survey you referenced. They may have made that evaluation primarily based on other factors they’ve assessed.
Furthermore, even if it was the survey that was the decisive factor in their ruling, the use of that for this purpose is not typical methodology of mainstream psak halacha among most poskim. It would be quite unusual, in fact. It goes against the grain amongst poskim, who would use only how the food is eaten among Yidden.
And as I mentioned earlier, there are poskim in America that still rule today like Rav Moshe, that one need not wash hamotzi when eating less than two slices.