I've got a 20g Walstad style tank that I've got stocked really heavily in order to get enough fertilizer processed for the plants. Diana grows plants so that she can have more fish..
Most of us prefer to have smaller groups of fish so they don't detract from the plants and aquascape design. Personally, I prefer to do it this way purely for aesthetic reasons, I don't like to be distracted by lots of fish swimming all over the place. Since most of us add chemical fertilizers we could technically have no fish in our tanks and they'd do fine, but the right fish can make an aquascape. Ghazanfar Ghori has what I would consider a high amount of fish in his tanks and they look wonderful, so there's no reason not to have all the fish you want in a planted tank.