Not true, actually. The Constitution allows states to apportion their electoral votes however they want. Almost all of them happen to use the winner take all system, but there's nothing implicit about how the Electoral College is "supposed to work".
To apportion the electoral votes of any State in a way that distorts the percentage of the votes in a Federal election would be a violation of the Civil Rights Act of 1964. "Winner-take-all" remains the least-messy way to assign electoral votes.
Thank god. Though the level of support it actually has is scary enough. Having a state as big and gerrymandered as Michigan operate like Maine or Nebraska in Presidential elections undermines democracy itself.
Because the two Congressional districts of Maine are similar it is unlikely that the shapes of districts would be the difference between a split of the state's electoral vote and the winner of the plurality getting all four electoral votes. In Nebraska, one of the districts is Greater Omaha, which is very different from the rest of the state... and the Third District is the last electoral vote that any Democrat could ever get.
Michigan is so gerrymandered that Grand Rapids, Kalamazoo, and Lansing are represented by Republicans. Draw the lines differently, and a district that stretches from Grand Rapids to Lansing would be majority-D; one that stretches from Kalamazoo through Battle Creek to East Lansing would also be majority-D.
