Replacement of ONE front shock.

I drive a Ford Ranger D/C XLT. Earlier this month, I was rotating the tyres on the vehicle at 90000km's. I discovered that the right front shock was leaking. I immediately went to my local Ford Dealership, who promptly and efficiently helped me. All the shocks were inspected and only the reported one wad deemed faulty. Ford replaced this shock under warranty, which I'm greatful for. On enquiring, it seems like only THAT shock was replaced. I asked if it's safe to drive a vehicle with a new front shock and one with 90,000 km of wear on it. I called another Ford dealer, who confirmed that it was their policy to ONLY replace the damaged shock. If Ford gave me the option to pay an amount for the wear on the healthy shock, I would have been willing to do so. Instead, I'm now driving a vehicle with one brand new front shock and one that has done 90,000 kilometers. I'm not sure how safe it is. According to Ford, it is okay to do this. I'm not sure if this is a healthy practice.