Last night, I was behind a Buick Terraza and noticed something strange. It had IRS. I thought all the GM minivans were a solid rear axle, and later in the trip I confirmed this by getting behind an Uplander. Sure enough, solid axle. A bit of research tells me that the Buick did indeed get a different rear suspension than the rest of the rebadges (they pulled the IRS from the Rendezvous).
Though, to be fair, the other rebadges got IRS if you ticked the AWD box on the options list.
This has been your pointless trivia for the morning, you may now resume your day.