The reason they did not do it is because they were first to the market with the power tailgate, and just didn't think of it. Once they came to market, others improved on it, and it was not probably cost-effective for them to change it midstream (though they did have a run of 7 model years).
What I wish they had done is to disable the power tailgate from the key fob when the van is locked. I am convinced the dent in my tailgate is from something bumping the button on the fob in my pocket when I was inside the house, and the tailgate opened and slammed into the garage door, before reversing.
The good news is that the 08 has a switch, right by the motor. Maybe Jason (or JCamasto) can order up one of those, once they come out, and retrofit it to work with the 4th gens.
2005 Dodge Grand Caravan SXT, 129K mi.
Former owner of:
1988 Dodge Caravan SE, 2.5L I4 (1988-1995, 99K mi); 1995 Plymouth Grand Voyager SE "Rallye", 3.3L (1995-2004, 169K mi); 2003 Grand Caravan Sport, 3.8L, (2004-2008, 106K mi), 2008 Nissan Quest, (2008-2010, 25K mi)
2008 Lexus RX400h (Dark Gray), 112K mi; 2005 Hyundai Elantra GT (Blue), 89K mi