Why do some planes have a cable from the top of the tail wing to the top of the fuselodge and others dont?

A lot of people will install thier radio antenna wire in that postion. That is the wire you see on some planes. Others choose to install their antenna wire in different locations.

Ken

Ken is right, sounds like an antenna wire to me. Many full scale planes have an antenna in that position, too.

Dr.1

I don't like to install my antenna in that position because it tends to snag on things when I'm loading up..instead I install mine inside the fuselage..or underneath
All up to the individual