クレヨンしんちゃんis a character from a Japanese cartoon. Since クレヨンis a loan word, crayon, it is written in katakana. Also, from a magazine interview with Tohoshinki, I found ライブ, singing live at a concert, radio, etc. It is written in katakana, because it is a loan word, too. It is interesting how Japanese people write in katakana to use loan words. They blend the words in as much as to make it sound smooth and not so foreign, but they write them in different alphabets to separate it from the other purely Japanese words. I think that this is how the Japanese people preserve what they already have and adopt new things. What amazed me the most as I learned more about Japanese culture by Japanese classes, by dramas and by films, is how much Japanese people strive to preserve their traditions. I can see that happening in usage of katakana for loan words, too.
Also, I don't see many differences among the explanations that the textbooks give. I think they say similar things, how katakana is used for loan words, for onomatopoeic words and for emphasis. The only differences are how much it left out one category or the other. Other than that, I don't see any differences among them.