I don't think that CNC machines can change the lifetime of an engine, and there is sometimes an inflated trust in what computers can do. Don't write off what was done in the past, I think they had a very good feel for what they were doing while lately we only get stuff machined in the far east under primitive conditions...
Plus OS was probably the first CNC engines, and it did not improve their life. Fox and Enya would outlast an OS, it was the harder metal, not the CNC machining. Now I think all engines are CNC, it makes for faster production, but especially for small lots such as model engines it does little to nothing for accuracy. In fact a hand machined engine made with care is probably better.