Why is a wife's touching of her husband's madhy forgiven out of need, while a man's caressing of his menstruating wife is impermissible, given the ambiguity surrounding the cases that are forgiven and those that are not?

The questioner should have referred to the two fatwas that he perceived as contradictory. There is no absolute prohibition on caressing a menstruating wife. The difference of opinion lies in the permissibility of enjoying what is between the navel and the knee. The correct view is the permissibility of enjoying everything except intercourse, based on the Prophet's (peace be upon him) saying: "Do everything except intercourse." However, it is preferable to avoid what is between the navel and the knee to avoid disagreement. It is permissible for a woman to touch her husband's penis, as it is part of the permissible enjoyment, provided that she avoids touching impurity and washes off any pre-seminal fluid (madhy) that gets on her, as it is impure.