It's also fair to say that most of Detroit's useful commuter ROWs are still in place -- not just to Pontiac and Toledo, but for example Ann Arbor and Port Huron as well. I remember when I mucked around with it, years and years ago, I discovered the only historic railroad ROW with commuter value in the Detroit metro that isn't around anymore is the one that heads towards the Rochester area.
With Ford putting major offices in Michigan Central, it's probably also a good time to look at returning it to active use as a major rail station. The Wolverine already runs into Detroit from Ann Arbor and out to Pontiac so you can pretty much start up two dedicated commuter rail routes for the cost of some push-pull equipment right now.
On a sidenote, I've always liked this idea:
http://fwrail.org/
ETA: Detroit is the 3rd largest MSA in the USA and Canada with no commuter rail AFAIK -- the only two that are larger being Houston and Dallas. There's no reason for that, either, when it has more resources for it than places like Phoenix or Las Vegas. All of the major Midwestern cities, in fact, have excellent commuter rail resources ... it's just a question of civic will, and perhaps a sense that a growing city needs better infrastructure.