The species are often seed grown and form large suckering colonies if left to their own devices. The hybrids - like Blanc Double de Coubert - and named forms are most often grafted to ensure they a) do not sucker aggressively and b) come true to form.

ETA: btw, 'Alba' is not a named form but just a variant of the species. Taxonomically, it should read Rosa rugosa var. alba, not R. rugosa 'Alba', as if it were a defined cultivar.