Is it safe to use copper pipe with natural gas?

My house is 40+ years old and has a natural gas hot water heater, stove, and furnace. There are copper pipes running through the attic to connect the furnace to the other two appliances and our a/c repair man recently told us it is unsafe to have copper pipes when using natural gas, based on the fact that additives in the gas will cause the inside of the copper pipe to corrode and flake off. Is this accurate and should I have the pipes replaced, or is he just trying to sell me something I really don't need? Please help!