In this Hanafi analysis, the maximum duration of menstruation is ten days. When bleeding ceases at that limit, the legal treatment differs, including discussion of marital intercourse before ghusl.
Cessation of blood and the obligation to perform ritual washing are not the same question. A particular consequence may be established before ghusl without abolishing the separate requirement of purification for prayer.
The rule therefore must not be reduced to a single undifferentiated statement that a woman is “pure” or “not pure.”