Each generation of computer power enables new AI techniques. Expert systems require explicit distillation of "rules". That took a lot of human work. And they are considered brittle when they are outside their expertise. But expert systems could on the million times weaker computers of the 1980s.

Watson employes statistical searching of large knowledge bases. You dont have to explicity ferret out all the rules and relationships. Google Translate does this too. There is no preprogrammed language dictionary.

The next frontier is deep learning which requires powerful computing to operate in real time.

All these techniques have their limitations. No magic bullet yet.