A few reasons:
- partly because in our societies, we're fortunate enough to be able to buy things if we want them (provided we can afford it of course).
- marketing (we MUST have it)
- it brings joy to people who are into this stuff (and if you're a member of macrumors, let's face it, we will be).
And while we don't NEED to upgrade yearly (I've always upgraded every two years but this time am upgrading after a year) I do think upgrading eventually, say at least every three years, in our society, is needed. We live in a world (fortunately) where doing things like using phones for browsing (finding info quickly), email, pictures, maps, is kind of necessary whether we like it or not. The iPhone 3GS did all of those things. But two weeks ago I was in a museum and someone asked if I could take a photo of her, so I did. It was a REALLY slow phone, the photo took a few seconds to take which sounds silly but it was odd. Thought "must be some old cheap android". But the software was ios and had the old school camera interface. Turns out was an iPhone 3GS or something. Now she NEEDS to upgrade.