I’ve maintained in all of my conversations about iPad sales that consumers treat the iPad more like a computer and less like the commodity device that sees iPhone sales continue to rise. - Jim Dalrymple
Commodity devices is a valid argument in markers where the iPhone is subsidized by the carrier. In the Belgian market full prize and unlocked iPhones are still the way most people buy their device, and aside from the early adopters I see a lot of 4(s) customers upgrading to the 6 than users that come from a 5(s).
I argue that customers expect their devices to last. A television has an expected life time of 5-10 years, a pc 3-5 years and a phone 2-3 years. At least that's what I experienced from selling Macs at a local Premium Reseller.
The iPad is a post-pc device, and most consumers see it as a replacement or alternative for their desktop pc. And I think customers logically expect the same longevity from their iPad.