This will vary from insurance company to insurance company and by state. Some insurance companies will allow one of the two people to purchase a policy without the other person, as long as that person signs an exclusion form excluding the other person from driving the vehicle. Sometimes, it will depend on how the two names are seperated on the registration. For example, if the registration reads John Q. AND Mary J. they may require it, but if the registrations reads John Q. OR Mary J. then they may not require. It up to the carrier to determine their liability and exposure. If it isn't a burden, then we recommend including all registered names as insured drivers.
Remember, you can follow this link for an online car insurance quote and possibly be able to purchase your policy immediately!!!