Dude. I never noticed that before about placing the word balloons in such a way as to force the reader to look at the art as they're reading, but you're totally right! I am at work right now so I can't check my entire comics collection, but conveniently, I do have Tokyopop's "Takuhai" magazine with me, which conveniently has sample chapters of 4 Japanese manga, and 6 OEL (Original English Language) manga[*]. Every one of the five Japanese artists (the 4, plus the Japanese artist for Princess Ai) uses this technique, while only one of the American artists does (Felipe Smith in MBQ). The American artists seem to place the text so as to avoid obscuring the artwork, instead of using it to guide the eye.

Fascinating!

[*] Of the titles sampled in this little zine, I've only read one, CLAMP's Legal Drug; I'm assuming that the sample pages in the magazine are representative of the various artists' work.