Way back in the stone age when I built plastic models, we used dawn to make 'washes' (mix water based paint with some dawn, brush on, then wipe off - fills panels lines and stuff, gives some depth, detail and weathering).
There's something different about dawn itself, because other soaps wouldn't work as well. Dawn seems to have more of the gooey stuff that's probably responsible for sealing the porosity in the rubber. Lots of cheap soaps seem to be heavier on the detergent and lack the thickeners/surfactants that dawn has.
