I think this isn't intentional. In EB usually troops that throw a javelin have charge bonus of 1. IIRC both Misthophoroi Hoplitai and Hoplitai Iphikratides are phalanx units that don't throw javelins, so their charge bonus should be other than 1. In this case I think the Misthophoroi's charge of 15 is actually the correct number. In other case, both usually fight in phalanx formation, where the charge bonus doesn't apply (IMO).