Utada stated that titles were important in making a song. How it is read was something she felt was important. Her example was "Final Distance" She wanted to to be read, FINAL DISTANCE. It's just something she feels need to be priority.

As for you question about the kanji, if the songs title is Japanese, it will be written in hiragan/kanji. Or in Sakura Drops case, katakan, but most often the other two.

Also, for THE WORKOUT, all of Exodus' songs were capitolized.
(In America, it all depends on the the printing of an albums jacket. There are often times when all songs are upper case and then there are times when they're all lower case)

We'll never know the true meaning unless Utada speaks more about. I hope I was of some help! =]