I've made lox and gravlax, I would have to check through old texts, but if I recall correctly the weighted 24 hour cure is to reduce the water content as the dry rub gets absorbed, which is slower than the brine. Reducing the water content makes a firmer, more easily sliced product. A brine has the advantage of being faster, and increasing the water content, which helps guard against drying out, and should lead to a moister, flakier fish. It isn't necessary, but it is cheap insurance.
pat