Transporting a Laser

That is true, never trust just the factory rack to hold the boat on. That is why I make sure I tie the bow and stern directly to the car not the racks so in essence the boat is tied to the car. The Thule racks on most SUVs just attach to the factory racks so you need to make sure the boat is tied direct. Scott
Obviously you should tie a large flat object like a Laser to more than just the racks themselves. You refer to the pullout strength of the factory racks, I was referring to the strength of the roof itself where the racks are attached, which is what I think the weight capacity means. The factory racks are often attached to the roof a short distance inside the edge of the roof. This means that they rely on the strength of the roof itself to support the weight. Aftermarket racks that attach directly to the car (and not to the existing racks) usually attach to the rain gutters or to a dedicated attachment point. The weight applied to aftermarket racks is carried by the sides of the car itself, which is why aftermarket racks have higher weight capacities.
Not sure what minivans you've looked at, but I can't recall seeing any with raingutters- just the full size vans.

I can tell you that the Thule racks with towers and feet that I have in my mini-van place the load in exactly the same location as the factor racks due - on the channel of the roof. I recall looking at at least 3 or 4 others as well, and all of them also place the load in the channel that the factory rack uses..