A cynical point of view could be that Apple is trying to reassert the equity of their master brand into their new offerings, as the 'i' prefix has begun to overshadow the master brand. But Apple rarely puts ego first and purpose second. So what is it?
Let's go back to the original 'i' prefix. It first appeared in the iPod. Which was quickly followed by iTunes. iTunes became the hub for iPod, iPhone, iPhoto and iMovie. Essentially an ecosystem built for sharing. Music, Pictures, Video, and Conversation...in a word, content. The enhancements announced for iPhone6 are all about this. Larger screen, better camera and video capabilities....all about sharing content.
Now let's look at Apple Pay and Apple Watch. These products extend Apple's footprint into two much more personal categories...finance and health. Categories where sharing is not necessarily embraced. Categories that might require a new, more private ecosystem.
So, perhaps the Apple prefix has a real purpose. During the course of the event today, Tim Cook kept talking about enriching people's lives. He also put quite a bit of emphasis on security and privacy.
Last, let's look at the invitation itself...'We wish we could tell you more'. This all points to Apple being a trusted confidant in your life.
So, clearly, i is for we, and Apple is for me.