K&R eventually did, even if they didn't at the very beginning. I also don't teach everything right away. But, if I'm going to teach the concept of looping, I'm going to teach the one that's easiest to grasp and fully know. That's a for-loop, not a .each method dispatch.
The concept of a jump is not one you want to ever teach, and I think you've chosen to go into more detail in one list than the other. In terms of "what does it do", both bits of code call "puts elem" on each element of the array. In terms of "what it's actually doing", the .each example is forming a block and passing it to a method, while the for example is a special syntax with its own scope implications. So the complicated parts of the .each version (blocks and method calls) are general concepts used throughout the language, that you would always want to teach to learners sooner or later. Whereas the complicated parts of the for example - the scoping and the for syntax itself - are dead ends that don't help you learn the rest of the language at all.
>The concept of a jump is not one you want to ever teach,
That is again another arbitrary social more invented by a rant written by Dijkstra. Learning that a computer processes code by using jumps is an important concept to learn, and it's actually a useful technique in many languages. Saying someone should never learn them is just stupid.
