Losi came out with the aluminum chassis for a simple reason. With today's very fast tracks with very large jumps, they knew aluminum wasn't going to break whereas it was a possibility with a composite. They added the side wings to add stiffness but to make sure things weren't any heavier than necessary. They didn't want people to just randomly bend the chassis and it still happens from time to time. They also discovered that with lipo's being lighter than older batteries, they could have a bit heavier chassis to make up the difference. This weigh is now lower than it was when the weight was in the battery which lowered the cg. Lipo's come in lots of different sizes and weights now though so a weight savings is debatable. Many still add weight though. Going aluminum was also cheaper than a carbon tub. Basically it came down to material strength and weight vs price and that's what they settled on. I think others are just arbitrarily copying them because of the "if it wasn't better then why are they doing it?" mentality. Some have gotten carried away with it.