I wonder if the "5" is a misdirection of some kind. Maybe they have 5 things to announce between iPod, Macs and iPhone?
I struggle with the 6th generation iPhone, with an A6 processor, running iOS 6 and 4G LTE being called the iPhone 5. With all those numbers floating around it seems like a marketing nightmare. I would have gone with "The new iPhone" -- unless Apple feels like doing that with the iPad caused confusion.
I have no idea why people online don't get this: The overwhelming majority of people would expect the new iPhone to be a 5. The name of the current model is a 4x, and the one before that is a 3xx. And that's all people remember. 3, 4, 5, right? Also, remember while products are new (and iPhones are), lower numbers are smaller - sounds like each incantation is around for a long time and will last more than the ~2/3 years.
99.9% of people on the streets neither know nor care what 'generation' the phone is, what chip it has, what iOS it runs. My step dad thought his iPhone was white because he forgot it has a white cover on it! Most people who use iPhones really have no clue about what makes them work, and that's a good thing, really.
Apple is a business and it's catering to what people want. If you argue that they should 'correctly' call it the 6, you're completely arguing against Apple's philosophy of making things simple and accessible.