Kernighan and Ritchie were well aware of Turing completeness. Dennis Ritchie started with Theoretical Computer Science before he wrote his first software (see http://www.gotw.ca/publications/c_family_interview.htm). You can be sure that designing C without Turing Completeness would have been for them like designing a car without tires.
Languages without Turing Completeness only make sense only in special applications because they are so limited (e.g. the C PreProcessor is not Turing Complete unless you use it recursively).
One of the marvels of the Turing machine is that it is so simple (you can describe what a Turing machine does on 2-3 pages) but it is as powefull in expression as modern languages with specification of thousands of pages are.
A lot of coders have no idea about the theories behind it. That is why a lot of code sucks. It's not the lack of Turing machines but on the theories that are connected to it (e.g automata theory, complexity theory).
What you are saying is like: I am tiler, i never check the foundation when i am building the roof, so it can't be important ;-).
You can make a living as a coder without all that knowledge. More than half of the coders do. But if you look at the people who shape the world of software (like Dennis Ritchie, Linus Torvalds, James Gosling, etc), you will notice they all are well versed in the area of computer science theories.
P.S. Concerning AI and Turing Test: computer games have no AI. The producers of computer games call their software opponents AI, but they are a collection heuristical algorithms cobbled together.
When you are playing agains an opponent, you can usually tell easily wether this is a computer or not. In fact, you are conducting a Turing Test then and the other side fails usually miserably.