Do you think this is a result of author's own attitude or rather the result of publishers' policies? Are the researchers unsure whether their measuring instruments are working perfectly or are sensitive/accurate enough? On the other hand we often see the results which are hard to reproduce, if at all, by others researchers...
Well, we cannot be ever 100% sure that our results are perfect or guaranteed, but this comment applies equally well to achievements "in favor" or "against" the tested idea.