Apple likes doing this kind of thing. It makes is kind of enigmatic. Like the old //gs, Granny Smith or Graphics and Sound. The 'I' also pulled in images of being an individual, also connecting back to their 1984 commercial, which was about being an individual. Other 'i' words were attached either overtly by Apple's add campaign, or by media pundits Independent, individualistic, intelligent, etc... This could of backfired, the 'i' could of been associated with all sorts of negative 'i' words, but that never really happend.