The RMAD and Windows System State backups are very similar. The key components that RMAD backs up as part of the System State is the Registry, NTDS.dit file and SYSVOL. During a restore (using the Repair Wizard), these components are restored to the DC, similar to what is done when restoring System State using Windows Backup.
Outside of the System State restore, RMAD has the ability to perform granular object or attribute restores which is not possible with Windows Backup.