The 42 was the first to incorporate prehensile technology. The other suits just open like the suit he uses when he first suffers a panic attack. Some or most of the other suits specialize in their own way. Starboost(Space Flight), Shotgun(Hypersonic Flight), some of the other suits also use these things but are prototypes for later suits etc. I don't think they advance each time, just like you said, I think each suit has a specific function or special tech to make it uniqueThat's exactly why it bothers me. You'd assume the later suits would be more advanced, and it says so in multiple media. The films just offer no evidence to support this. All his suits from MK7 to MK41 seem like they can do exactly what the 42 is trying to do, yet they actually work, and don't fall to pieces when they're hit with a truck.
They all use arc reactor tech, they all have repulsor weapons, flight capability and uplink to Jarvis/Friday. I think he occasionally upgrades certain aspects of the tech with newer suits, such as the arc reactor tech or the lasers(MK6 was one time use, 7 was more powerful, and it looked like the 45 could use them continuously..
Edit: Bones was the first to be prehensile. It was a prototype for the MK42