There are plenty of differences, but they're of various importance. One fairly important one is Campy vs the rest of the guys. Best I can remember, Campy use a slightly different anchor button ("head"), so a generic cable may jam in a Campy shifter. Haven't heard of any critical consequences of using Campy cables in Shimano gear.

They're available in different lengths too. Some stuff intended for MTBs isn't long enough for full-sized road bike RDs.

Then you can have stainless or galvanized cables, they can be merely spun or spun & die drawn, a couple of different surface treatments to make 'em slicker.
Most casings these days are lined, but there's still some noname, generic stuff out there that isn't.