Just heard in the latest Penny Arcade podcast (at about the 8:28 mark) that the Fighter's expertise dice mechanic might apply to other classes later on. This was in reference to Jerry asking if there was a "grant a +2 to your friend's attack" use for expertise dice... and Mearls responded that it depended on what they do with the Warlord, "as this mechanic might show up in another class too".
Thus, there's no guarantee it will remain a Fighter exclusive mechanic, and instead might become more of a martial combatant mechanic (the same way the spell mechanic is not for any one class, but for multiple classes that can cast spells.)
Thus, there's no guarantee it will remain a Fighter exclusive mechanic, and instead might become more of a martial combatant mechanic (the same way the spell mechanic is not for any one class, but for multiple classes that can cast spells.)