Why must it change to be good? It's dub, that's how it works. It's the rhythm, it's the bass and effects, the overall production, which makes it good. Rhythm & Sound can hold its ground when compared to the earlier Jamaican dub legends such as Lee Perry and King Tubby.
Sometimes dub can have vocals, but originally not as they are usually instrumental versions, or "dubs", of reggae tracks that were added on the flipside of singles. The producer emphasized the beat or "riddim" and added all kinds of effects such as echo and reverb and employed a myriad of different production techniques, some of them quite original like putting beeswax on the playback head on the tape deck or burying the tapes in the ground for weeks to alter the sound.
Basically the early dub producers in Jamaica was using the studio itself as an instrument, the whole dub thing went on to become a genre of its own over the years, which Rhythm & Sound is a part of with a slew of other artists.
This German duo had already made a name for themselves during the early 90s when releasing a series of 12"s under the name Basic Channel (and later another series of 12"s as Maurizio) where they mixed the dub aesthetic and production techniques with the German techno of the time, which would become a form of techno on its own, surprisingly called dub techno.
This went a bit long but hope it clears up something.
