The wife earns a large salary: must the husband still provide maintenance?

Yes, a wife's maintenance remains obligatory on the husband even if she is wealthy or earns more.
The duty of maintenance arises from marriage, not from the wife being poor. Allah places the responsibility of providing maintenance on men as part of their leadership. A wife may voluntarily waive part of her right or help her husband, but that is her choice and kindness, not an obligation. Maintenance given by a husband also counts as charity and earns reward, even the morsel he places in his wife's mouth. See Maintenance (nafkah).