I thought the accent was to indicate to English speakers that the word has three syllables rather than two? The acute accent isn't standard for marking a long vowel in romanised Japanese (it's usually a macron or a circumflex, or a doubling of the letter in ASCII-only contexts); and as best I can tell, the vowel in the original Japanese is short -- so closer to the "e" in "bed" or "met" than to the "ay" in "okay", if I understand correctly.