If I am not mistaken the canton you live in also has a bearing. IIRC people with VS plates are most likely to have an RTA in Switzerland.

Also, health insurance is also more expensive in some cantons than others.

Insurance is all about statistics...in some cases that includes the issue of nationalities. Unfortunate? Yes. Discriminatory? Strictly speaking yes. Wrong? No...because that is the nature of insurance. People with a higher likelihood of filing a claim pay more. Fine by me.