It is logical not? How can you make sure that resistance is not open? When you are working with these types of tensions you cannot take anything for granted or for sure, it never hurts to make sure of things and respect good procedures, because these are to avoid a greater evil. And also as you say in case everything is fine, the user starts testing the open equipment, as you will expect not to give him curiosity and put his hand where he should not. A warning with good intentions is never wrong.
Mauro is right 740923, by procedure I discharge the capacitor before putting a hand and in some cases they were loaded.