You're right. But that's a "reasonableness of restriction" issue, not a "continued employment supports new promise" issue.

On the latter, as the Ohio Court recognized in reaching its decision
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Jurisdictions throughout the country are split on the issue presented by the certified question. See, generally, Annotation, Sufficiency of Consideration for Employee's Covenant Not to Compete, Entered into after Inception of Employment (1973), 51 A.L.R.3d 825. As summarized by the Supreme Court of Minnesota, "cases which have held that continued employment is not a sufficient consideration stress the fact that an employee frequently has no bargaining power once he is employed and can easily be coerced. By signing a noncompetition agreement, the employee gets no more from his employer than he already has, and in such cases there is a danger that an employer does not need protection for his investment in the employee but instead seeks to impose barriers to prevent an employee from securing a better job elsewhere. Decisions in which continued employment has been deemed a sufficient consideration for a noncompetition agreement have focused on a variety of factors, including the possibility that the employee would otherwise have been discharged, the employee was actually employed for a substantial time after executing the contract, or the employee received additional compensation or training or was given confidential information after he signed the agreement." (Citations omitted.) Davies & Davies Agency, Inc. v. Davies (Minn. 1980) 298 N.W.2d 127, 130.
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and, btw, nocnik, all is not lost. The Ohio Supreme Court did not find in favor of the employer. It sent the case back down to the lower court to determine whether the restrictions were reasonable.