The legislation seems a smart "power-law" approach (I'll let Malcom Gladwell explain) to weed out problem drunk drivers.
Of course, such action could implicitly condone "normal" drunk driving -- "Not Super Drunk? Not a problem! Welcome to Michigan!" -- but as long as regular drunk drivers face appropriate penalties as well, this should not perversely incentivize slightly-less-inebriated cruisin'. And we must remember that there is a social cost in teetotaling killjoyism as well.