I would not say "stronger." They are more stable. With a front drive car the power to the wheels is on the front wheels. This is where the engine weight is located. On rear wheel drive cars the power is on the rear wheels where there is less weight.
There are also products like the Shurtrax traction device that allows you to put additional weight on the rear wheels. They have models for both pickup trucks and cars. It is a simple system that lets you put water in an bladder (much like a waterbed) and let the water freeze or just remain in the bag and add traction for rear wheel drive vehicles.
You can buy Shurtrax at http://Shurtrax.com or a site like http://trucktoys4less.com/shur-trax-link.html. The product costs between $69.99-$139.99 and can add 400 pounds to the rear of a vehicle.