There are several reasons why this is the case.
To start with all the money to develop better engines moved to jets and turbo props in the 70s and 80s, and all the good people went with it. So there really hasn't been a lot of development in piston engines since then.
The newer aircraft on the market are things like the PS28, or sportscrusier. These use more modern materials to keep the weight down, but they just aren't as robust, and have a lot of undercarriages collapse.
Maintenance on aircraft is very different to cars, so a 30-40 year old PA28 is going to be in far better condition than a car of the same age.
You're best bet for a new aircraft is to find a school with either a PS28, or possibly a cirrus SR20, but these will be nowhere near as robust, have quite poor engines, and don't really make very good training aircraft at all.
I don't see why it's confusing that the warrior 2 and warrior 3 have the same name, it's no different to cars. They're making the 7th ford fiesta now, but it's still got the same name.