Although there are also 5-string basses that add a high-C string (so E-A-D-G-C). But in reggae the low-B is more common. And then there are even 6-string basses, with both low-B and high-C. These are mostly used in jazz, I think, and you need big hands to play them
I think you can argue about the advantage of a 5-string bass. I guess it's correct to say that all classic reggae bass lines from 70's/80's were played on 4-string basses, and the perceived "heaviness" of a bass line is often more determined by the relationship between notes, articulation and resonance, than by actual pitch.
About Leroy: I recently saw him at the Reggae Geel festival in Belgium, where he also did the classic bass lines intermezzo. It's when a guy like him casually picks up the bass, when you realize how gifted a musician you actually have to be, to be able to play a "simple" bass line like Full Up with such vibes. I mean: the bassie of the band that was backing him was doing a good job in playing all the well-known bass lines "correctly", but as soon as Leroy took the bass something magical seemed to happen. Or at least that was how I perceived it, there and then