Hi Scott,
In my experience, the traction of my RWD Mustang is not sufficient in any snow. The FWD minivan does much better in our subdivision.
Apples and oranges. :-)
Your Mustang probably has wider "performance" tires while your minivan has narrower all-season tires. Your Mustang has lots more torque than your MV. And, your Mustang has little weight on the driving tires while the MV has lots. If your Mustang is a manual transmission car and while your MV is an automatic, that makes a difference too.
It's not just FWD vs RWD. :-)
Tires make a big difference as stories in Car and Driver and the like make clear. [link|http://www.hehd.clemson.edu/PRTM/special/GH/Drive.htm|Here's] a nice cheat-sheet on driving on snow. [link|http://www.epinions.com/content_41628634756|Here's] an epinions piece talking about the wonders of Blizzak snow tires on a 1995 Mustang in Michigan.
Cheers,
Scott.