What’s the deal on inference engines versus non-inferencing rules products?

The Gartner magic quadrant, and many writers on this topic, differentiate between inference engines and non-inferencing engines. An inference engine basically figures out what information is needed and in what order rules have to be executed in order to achieve some goal. It relieves programmers of a lot of burden in constructing their applications and makes maintenance much easier, since you don’t have to worry as much about dependencies. A non-inferencing engine slams through rules in a set order, which can be fast but inflexible.