What more could they say? Do you want the name of the rep who made the mistake? Do you want them fired? Neither one of these seems remotely reasonable, but I'm not sure what else you could want.
It was a simple human error. Customer service agent was wrong about the policy. It happens.
You are making an assumption that it was human error. If it in fact was human error, they could state that and say that they also searched their database for the words Linux to make sure this hadn't happened with other reps.
[Added]: They could then make a public statement about the amount of times it had happened and the total refund they issued. If it happened to 100 users at $1,000/per user, then they could issue $100,000 in total refunds. Further they could state that installing another operating system does not ever void the warranty.
You are making an assumption that it was human error. If it in fact was human error, they could state that and say that they also searched their database for the words Linux to make sure this hadn't happened with other reps.
[Added]: They could then make a public statement about the amount of times it had happened and the total refund they issued. If it happened to 100 users at $1,000/per user, then they could issue $100,000 in total refunds. Further they could state that installing another operating system does not ever void the warranty.