Silvertwinkie -- I looked at the site you gave and it said the 2004 Explorer was "under review" and it didn't give a rollover rating.
For the 2003 models, the 4X2s and Sport Explorer got a "2" rating, but the Explorer 4X4 was rated "3". Maybe I was looking at the wrong place. I looked at these numbers recently while comparing the Explorer to the 4Runner and was surprised to see that the Sport Trac actually scored lower than a regular Explorer 4X4.
I think that if you look at a lot of SUVs, no matter the length or tow capacity, you'll find that the rollover rating isn't all that great. I was mainly concerned about the rollover rating for the times when I have nothing in tow (most of the time) and I'm only carrying precious cargo -- the kids!