For the sake of accuracy, there are MS69 Morgan Dollars. Oops, sorry Numis-addict, I see you already covered this.
Based on the NGC website you are correct but I think that NGC should rethink that policy. There policy is that a coin that is CAMEO with one side ULTRA CAMEO qualifies for the star designation. That should make the grade of PF70* CAMEO possible even if they say it is not. Likewise, a proof coin with one side qualifying for CAMEO should be a PF70*.
Um, if no coin can be a 70 then it's a 1 to 69 scale not a 1 to 70 scale, and then people would be arguing no coin can really be a 69... you can see where that leads. Any scale has to have its entire range used or what's the point? NOT awarding 70 to any coin is what would destroy the meaning of the scale, because 70 means nothing if no coin can possibly achieve it (and although it's already been said it bears repeating: 70 DOES NOT mean perfect).