Most spouses who are both eligible for medical insurance through their employers determine which plan is most cost-effective for them and/or which coverage is most beneficial to them.
If your wife's health-care coverage is what you want for any reason, that is fine. But, again, your employer is not obligated to pay you for making that decision, even though it saves your employer money.
Keep in mind that more and more often, employers that offer medical insurance require workers to opt for their spouse's coverage if their spouse is eligible at another company.
Some employers do pay some offset to employees who opt to buy their own medical insurance coverage through other sources. Usually it is a standard amount based on how much they pay for their portion of the cost of single coverage for their employees.
However, this is totally an option that the employer decides to do in the spirit of employee relations. It is not legally required nor an industry standard practice.