Rear Suspension Shock Absorber problems of the 2006 Ford F-150

I discovered a leaky rear shock absorber on my 2006 Ford truck while still under warranty. I took it to my dealer who confirmed that the shock absorber was defective and would replace it, but not the pair. Every professional shop that I have spoken with, to include the Ford dealer, says shock absorbers should always be replaced in pairs, but Ford refuses to replace the pair--it says it will only replace the defective one. I appealed to Ford motor corp and they too refused. I believe that is wrong and unsafe.