The correlation is indirect.
Biomedia is colonized by N-bacteria, which help break down ammonia before it can fuel algae blooms. In a planted tank, the plants themselves provide the bulk of the biofiltration in a tank, between the leaves and stems also providing a surface for N-bacteria to colonize and their own absorption of ammonia to provide the nitrogen they need for photosynthesis.
One of the reasons I advocate good flow in a tank is to help prevent dead spots. The plants also break up water circulation through a tank, which can lead to even more dead spots than in most non-planted aquariums. Dead spots accumulate debris, and decaying debris building also tends to lead to algae issues.
I usually encourage people to incorporate as much mechanical filtration in their tanks as possible, as in a heavily planted tank the plants themselves can carry the bulk of the biological and chemical filtration. Plants produce TONS of debris though- and lots of mechanical filtration can help reduce the amount of manual cleaning (pruning, siphoning, etc) that it takes us to remove all that debris before it becomes algae food. Just have to clean the filters.