To paraphrase the comment above that line, they say its purpose is to avoid accidental assignment. That's not an issue with "not equals" though, but that may just be their point.

As for whether it's more readable, I'm skeptical: It may save you going through some of the condition, but I believe getting used to it would make you more likely to overlook parts of the condition. Plus, the way it reads is the opposite of how you'd say what it does in English.

F̶i̶n̶a̶l̶l̶y̶,̶ ̶o̶b̶s̶c̶u̶r̶e̶ ̶a̶r̶c̶h̶i̶t̶e̶c̶t̶u̶r̶e̶s̶ ̶m̶a̶y̶ ̶d̶e̶f̶i̶n̶e̶ ̶a̶ ̶n̶o̶n̶-̶z̶e̶r̶o̶ ̶N̶U̶L̶L̶ (see to3m's reply). Using NULL makes it easier to find null pointer checks and conveys semantics (pointer vs integer).