I have been on both sides of this.
I was riding home from work one day on my motorcycle. Suddenly, my oil light came on, and when I pulled off onto an area on the shoulder I saw an oil trail behind me. One of my lines had ruptured. It was getting dark (about 9 pm in the summer), and my cell phone was nearly dead. I called my husband (who wasn't able to help me that evening), then called AAA. My bike had a Voyager Kit (think 'training wheels'), so it could actually be put on a roll-back and didn't need a special truck. Unfortunately, the first dispatcher I had talked to neglected to pass along that information. It was the 4th time I called when I got a different person, who finally got a truck sent out to me.
I was there until 3 AM. By myself, on a lonely stretch of road. No one - not even other bikers that went by - stopped. Really made me feel sorry for the state we've come to, where no one will even offer to help.
I always stop for a lone bike that's stopped on the side of the road.
There was a woman whose car stalled at a light a little before my 'adventure'. I was on my bike, and while people were passing her and honking at her, I pulled up behind her. She had a pretty small car. I asked if she needed help, and she said her husband was on the way - she was just upset that people were so impatient. I offered to help her get the car to the shoulder. Once we went to try to push her car, a car full of young adults pulled over and helped us get it off the road.
If I am by myself, and I see someone that looks like they're having car trouble, I will pull over and open the window a little bit and ask if I can call help for them. I won't open the window enough for them to get an arm in, and I leave the car in drive - but I do offer. I know what it's like when you feel stranded and no one wants to help.