I've personally helped out several people over the years who needed a pull or push back onto the trail or righted. And, I've received help from others more than just a few times. However, I can think of possibly three situations in which I may not provide assistance: if the vehicle is stuck off trail due to the driver having done something illegal, the driver is obviously drunk, or the stuck vehicle weight is greater than 5000 pounds or buried in deep sticky mud. These are just some rules of thumb, nothing carved in stone, here.
Only once have I not offered to assist; the driver of the stuck pickup truck with camper unfortunately did not take it well, even though I offered a ride to wherever he needed to go to get help. <img src="/forums/images/graemlins/frown.gif" alt="" />