The bottom line is that Apple have to stay ahead of the competition ("What competition" I hear some of you say).
With the usual pre-Christmas plethora of new devices they just want to offer a USP (unique selling proposition/point).
Any company worth its salt will react to competition in an aggressive way, even if it is partly to the detriment of its existing customers. It happens everywhere. It's not just Apple trying to elicit an additional purchase from recent purchasers.
If you are happy with what you have and a new OS isn't going to make that much difference, then fine. If you have to have the latest, greatest offering then you have a problem... irrespective of what technology floats your boat.
If I were a business owner having just shelled out a bundle of cash for multiple devices... I suppose I would feel somewhat screwed, but this is what happens in the world of technology, and will continue to do so at a rapid rate.
Life's like that. Budget for device life expectancy and you won't be overly disappointed.