If you guys can find a TV station that plays the "Music Voyager" series, you can see a good explanation and demonstration from none other than Ernest Ranglin, Sly Dunbar and others. "Music Voyager-Jamaica".
One more thing. The term "Rockers" is more associated with an "era" and sound of reggae music than it does to a specific beat (Think Jacob Miller, Burning Spear, the Rockers movie, et. al).
True, rockers is associated more with a steppers beat, but pretty much all reggae music from circa 1974 up to around '78 or so was known interchangeably as "Rockers" or "Reggae". The sound changed again, especially when Sly & Robbie started Taxi and had a string of hits with Black Uhuru, Dennis Brown, Jimmy Riley (Tarrus Riley's father) and others. As a sidenote, "Guess Who's Coming to Dinner" by Black Uhuru uses a Steppers beat, but NO ONE would ever refer to that song as "Rockers".
As far as counting beats, most Jamaican reggae musicians use the bass drum as the reference. That's just how it is. And don't forget that in One Drop, the snare (rimshot) is the SAME beat as the bass drum.