I think that the "ZX" designation is applied according to the following:
"Z" = Road.
"K" = Off-road.
"X" = Competition.
Out of that you get ZX-6/10/7/2, whatever, and KX250/125/60/80/500, whatever.
You can argue that bikes like the ZX-11 and ZX-6E (ZZR-1100 and ZZR-600 respectively) aren't competition bikes, but they were when they were new.
Suzuki have a similar thing for their models. GSXR isn't just a name, it's an actual model designation according to what the bike is.
I think "G" indicates 4-stroke, "S" = twin camshafts, "X" = 4-valve head, and "R" is something I can't remember, but probably has something to do with road or race-replica.