Well, there's no real universal script, so it's not like a better encoding basis (besides numbers) could be found. And dropping down to Latin script is done for other reasons, too. Probably even on the same page.

Encoding in Kanji would result into fewer characters, but would probably result in some funny phrases. ("Turn left at Ephemeral Outhouse!"). Not quite sure whether that's good or bad...

Ditto for X, Y, W.

I guess they'll just have to use their convenient systems for entering ASCII then huh.