Do I need to replace my copper gas line before installing a new dryer? Why?
Sounds like a liability issue. If they hook it up and the line breaks or leaks, they can be held liable. They probably want a gas flex line (something like this) installed between the copper and appliance.

If I were you, I'd get a gasfitter out to have one installed and hook up the appliance (which means future deliverers will install it). You don't want to be wrong on a gas line.