I have to agree with you, and at some point I would have gotten myself some animals. I considered that at the beginning of the story, as they are in farm country, and it seemed like a logical move. But then I considered that the zombie would simply kill all of the animals at some point, maybe in frustration at not being able to get at the people, or just because he could; and I decided I didn't want to write about that.
Caution is different from refusing to take risks. I think the guys have taken a number of risks, but at least considered them. The thing with the aircraft is definitely a wait-and-watch thing. In their place, I would no more grab a radio and immediately attempt to contact a passing plane than I would step out into the road and flag down a passing vehicle. Especially if I could not determine what sort of plane it even was. Not knowing what happened to the world, I would consider everyone not in my own group a little suspect.
Maybe that's a tribal mentality, but trust of strangers would be the first thing to go if civilization crashed. The world is just chock-a-block full of idiots, crazies, and outright killers. Without the restraints of civilization in place, I would expect them to follow their urges. And I do not intend, ever, to be the victim of some savage's urges.