Summary:
We can derive חריצין ונעיצין from בור, but not אמת המים ונברכת הכובסין; it is usual to write שיח ומערה together with בור (even without a צריכותא); however when the פסוק writes בור exclusively, the משנה (when referencing this פסוק) needs a reason why to mention שיח ומערה.
Summary:
סלעים in the משנה refers to rocks, not copper coins since they are not found near walls. When differentiating between different rulings we prefer to make the difference as narrow as possible.