The difference is that there’s a competitive Republican primary in South Carolina, and our votes are needed there. Kos suggested this plan for Michigan because the DNC is not going to seat the Michigan Dem delegates anyway, in retribution for Michigan having moved the primary date up against the terms of a prior agreement. As a result, the major Dem candidates aren’t contesting Michigan. Since their votes in the Dem primary are essentially meaningless anyway, Kos recommended Dem voters messing with the Republican primary.
Obama is not on the ballot but I'm fairly sure that clinton is. How much would you like to bet that the DNC will rescind its refusal to seat the Michagan delegation if she needs their votes (i.e. the 'super delegates' aren't enough to swing the nomination to her)?