An incrementing product revision number is a bit boring, but certainly nowhere near those depths of marketing misery.
[1] This example is semi-fictional because nobody could possibly remember the actual model numbers from that era.
I'm more worried about the original iPad Air still in the lineup. I've got an ipad2, and it's feeling old and slow (without having a newer one to compare to). That's not going to be a long term good purchase.
Now they could afford to, but they don't. Yes, it takes effort to keep those old lines running, but the guys doing that needn't even talk to the ones designing the new versions and the software running on it (those older generations get left behind, OS-wise, don't they?)
Also, today cases and accessories rely on Apple form factor as a platform on which to build - and that's a huge market, and important for consumers and 3rd party vendors... I'd like to think my iPhone6 case (if I owned a 6) would fit the next year's model.
iPod nano with 5 different form factors in 8 years? Ain't nobody got time for dat no more.