Wire and rebar do not make the concrete stronger. It holds it together when it cracks. If they have a really good slump when they pour the concrete, odds increase dramatically that you will have very minor cracking. All concrete cracks, that's a given. The wetter the concrete, the more it will crack. There is a point where it's too dry and they cannot spread it, but that's almost impossible with cement trucks. The only way to stop them from adding water and making it into soup is to stand there and tell them how important the slump is to you. They know, but they don't want to spread it without extra water. All the water does is make it easier for them to spread it. Easy means faster. They get done sooner, get paid the same amount, and have an easier day.
en.wikipedia.org
The big advantage rebar has over wire is that it is held up in the air with chairs, and the concrete completely surrounds it. If it was possible to lift the wire and for it to remain in the middle of the concrete while everyone is walking on it, wire would be better then rebar. What usually happens is they start the pour and a guy will lift the wire while the other guys are spreading it. Then two guys will grab a screed board and start leveling the concrete while just one or two are spreading it. The guy doing the lifting gives up on that and will start spreading because they don't have time to pretend to lift the wire when it just ends up in the dirt while they walk on it. You get some pictures of them lifting it, but before it's halfway done, that isn't happening any more.
100% of every house that I've worked on with wire in the slab, and cut through the concrete to move drain lines, has had the wire on the dirt. In the last 20 years, that's probably been close to 50 houses, or more. Wire is very common in older homes around here. It was an idea that was tried, and failed. Now it's not allowed anymore. It's just not possible to keep the wire in the middle of the slab.
