I think you're mixing up the written test ("knowledge test" in FAA parlance) with the practical test. On the written test, they ask a lot of questions, and you must answer at least 70% of them correctly to pass -- very mechanical, very straightforward.
On the practical test, the PTS lists all the areas and tasks on which you must be tested, and the DPE must test you on each one, and every one of them must be performed satisfactorily. In that sense, the passing grade for the practical test is 100%, and the examiners are all required to conduct the test according to the applicable PTS -- nothing left out, nothing more added in. However, "satisfactory performance" on each task does not require perfection on each task.
Each task has tolerances, such as airspeed on final staying within +10/-5 knots of desired speed. As long as you stay in that range, your performance is satisfactory. Unsatisfactory performance on maneuvers like that is defined as "consistently exceeding tolerances stated in the Objectives" and "failure to take prompt corrective action when tolerances are exceeded." So, if on one approach you get 12 knots fast, you still pass if you promptly correct the speed and don't make the same mistake on the next approach.
So, in terms of practical piloting skills, you must demonstrate knowledge and competence (but not necessarily perfection) on every one of the skill the FAA requires for the certificate/rating you seek in order to pass the practical test for that certificate/rating -- no "70% rule" on that.