プロフエッサーX/Professor X
This katakana word is a loanword from the english show X Men. This is a poster for the Japanese anime version of X Men. This is especially interesting since this show is borrowed from America yet a Japanese spin is put on it. Also this version has even added an additional character, 市木久子, her name is in Kanji but everyone else is in Katakana. I believe that this serves a special purpose in that Japanese viewers of the show will be able to directly identify with her and retain a sense of pride in their nationality. Also with the use of Professor X. The Japanese already have a word for Professor but probably choose to retain the English word in Katakana that way they preserve the popularity of X men.
ジャンプアルテイメットスターズ/Jump Ultimate Stars
Strangely enough this katakana comes from putting together a whole lot of Japanese characters into one game. This game isn't planned on being released in the US because of the licensing issues between the many characters in the game. It is strange to me why they use katakana. I think it is to preserve the brand name of Jump (from Shonen Jump). I think Katakana serves here to create a clear and cohesive title. The developers probably prefer "Jump Ultimate Stars" to "Great Stars that can jump."
The different books describe katakana in different ways because after the more obvious reasons, onomatopoeia and loanwords, it is difficult to tell exactly why. In the Jump Ultimate Stars example it is difficult to tell precisely why they would use katakana over anything else. Since this is ambitious it is hard to tell why they would use it over anything else, but it is definitely nice to have a written style devoted wholly to this concept.
