I don't think it's "dying". Tablets are in the same situation as flat-screen TVs: the market is more-or-less saturated, they last a long time, and there is no compelling reason to upgrade. In contrast, phones have a fairly short replacement cycle, because they are subject to significant wear and tear, and there are compelling advancements in power utilization, communications, etc.
And I think Apple managed to avoid the same happening to the iPhone by introducing a new size category.
It's actually incredible just how fast and new the iPhone 5 feels even today. I was perfectly happy to stick with it until the new sizes came out (admittedly I haven't bought a new iPhone yet because it costs money, but a lot of my peer group has).
The subsidization by networks is key in keeping people in a short upgrade cycle, and reducing the likelihood of switching to a cheaper Android phones. It's no doubt Apple people would upgrade much less often if they to shell out $600+ for unlocked phones every couple years.
