Romneycare is a law on the books, what Bachman said was an unfounded allegation. If Perry did break a law then he should be convicted, but Bachman should’t just throw out allegations. That’s the difference.
What Bachmann said is a 100% accurate description of the appearance of a conflict of interest. Since laws allow such conflicts of interest, it's up to each voter to decide whether the conflict of interest was improper.
And candidates in any primary will always make criticisms of opponents that the other party can use in the general election. Has always been that way and always will be.