The Ares-I is not designed to be an ISS ferry. It is part of the 1.5 launch architecture to return to the Moon. Actually, I think NASA regards it as a development program to obtain the Ares-V hardware in an incremental and thus affordable way. This makes a lot of sense. When it turns out to be too expensive to maintain 2 rockets for the Moon program, they will simply man-rate Ares-V and cancel Ares-I. ISS will be left to US private enterprise (COTS). Well, at least that's the plan.

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