I have an iPhone 3GS and have waited for the iPhone 5, which I will get. If you're someone who tends to skip a model, I can't help but think that the iPhone 4 and 6 cycle is better than the iPhone 3GS and 5 cycle.
I believe you are 100% correct. Although I've never skipped a model, there's not much Apple could include in the iPhone 5 to compel me to buy one, so for the first time, this will be the one I gloss over. The iPhone 5 simply will not be an earth shattering new model.
That's not to say that it won't be a good phone, especially for those that are either new or running with a worn old model. I do believe the iPhone 5 will merely be a placeholder till the iPhone 6 is released.
Because sales are already so robust with the existing iPhone 4, it's only a matter of maintaining some growth via the iPhone 5, till iPhone 6 becomes the next desirable model.
Same goes for iPad. Early days I know, but which cycle is (likely to be) better, the iPad 1 and 3 cycle or the iPad 2 and 4 cycle?
Having both the iPad 1 and 2, I find that each has it's advantages. Yet that said, I greatly prefer my original iPad. It's built better, has no light bleed (I've exchanged three iPad 2's) and they all have varying degrees of what appears to be a cheaper display that bleeds light, period.
As far as iPad 3, if it has a higher resolution which is widely rumored to be the case, then that alone will make it worth purchasing.