The problem as usual is the media. Someone living in a basement came up with that (hideous IMO) iPhone 5 design and moniker, and the media took it as fact. Due to the insane number of rumours that random unconfirmed chinese sources provided, many took the existence of the 5 as fact; but when Apple didn't introduce it people were disappointed. If that fake iPhone 5 was never drawn up, people wouldn't feel so let down by a phone that looks the same as last year's version. Soon the media will hype the iPhone to have something utterly stupid like a flying carpet feature, and then everyone'll be disappointed when in reality it doesn't.
I have no doubt that Apple is working on a new design, but a new one every 12 months isn't sustainable. The iPhone 4 has a pretty much perfect design as it is now, there's only so much you can do to improve a design. How do you improve on perfection? I'd say the rumoured full aluminium backed design similar to iPhone 1 won't happen. Signals don't penetrate aluminium too well, unless perhaps they use the aluminium back as the antenna.
I have no doubt that Apple is working on a new design, but a new one every 12 months isn't sustainable. The iPhone 4 has a pretty much perfect design as it is now, there's only so much you can do to improve a design. How do you improve on perfection? I'd say the rumoured full aluminium backed design similar to iPhone 1 won't happen. Signals don't penetrate aluminium too well, unless perhaps they use the aluminium back as the antenna.