Michigan DOES require a license for painting contractors. You can have either a residential builders license, which covers it, or just a residential maintenance and alteration contractor license for the painting trade.
Here is a place to start:
http://www.michigan.gov/dleg/0,1607,...4259--,00.html
It's kind of funny, but you can move the house, pave the driveway, drywall it, install the fencing, install the sewer line and septic tank, install the lawn sprinklers, and carpet it or install vinyl flooring and you don't need a license. But if you want to paint it.... You need one!