(This isn't hardcore physics, but bear with me. I've been watching too much Highway Thru Hell and I'm curious about this)
A common problem on the Highway Thru Hell TV-show is trucks stuck on an icy road that cannot make it up a hill. So the towing company sends a towtruck to pull the truck up the hill. What I'm wondering about is how exactly a towtruck can pull a truck up the hill. I somehow doubt the towtrucks simply have better engines or tires/tirechains to prevent wheels from spinning out, and with the additional equipment they carry they are pretty heavy in and of themselves. And even if it was due to better engines, why don't manufacturers build trucks with these better engines so they can keep driving on icy roads.
So how exactly are towtrucks able to pull trucks up an icy hill?