So when a new pc gpu, iPad or whatever non console hardware comes out you don't hear how it will take years for coders to understand this new hardware. Instead new stuff supports it right away.
That's not completely true. Old techniques are used until the new hardware has a large enough install base to worth targeting directly. Ergo, your new hardware runs the old code just fine, and devs can make new content for it, but it's not used to anything like its full potential for some time after release, as the lowest common denominator is last gen HW. That's not true of traditional consoles that, as closed boxes, also get targeted as a complete unit.
By the time developers "come to grips" with typical console hardware you would have been able to release multiple versions of hardware abstracted bc hardware to where any technical advantage of the old world console hardware is totally lost.
Except that comes at added cost buying new hardware. In the traditional console, you certainly get your money's worth when every ounce of performance is squeezed out of it. With progressive hardwares, improvements come more with buying new hardware than devs advancing the software, although of course software developments do help.
Hypothetically, let's imagine MS released a BC console. Moving to compute based rendering would probably be slowed down versus releasing a completely new hardware with no legacy ties.
Now if continuing consoles are fully BC and get refreshes every two years, as new techniques are developed (like tessellation was) they won't be fully implemented on the new hardware as the old hardware is the primary target. This is the problem with PC and mobiles - new hardware with new techniques goes unused. That's where console's greater hardware utilisation is a big win.
Obviously the change in the market and cross-platform middlewares means new boxes aren't viewed in isolation, and personally I think the move to abstracted hardware makes more sense than the fixed box paradigm. And as a result, getting better results warrants smaller, more frequent hardware upgrades rather than the 5+ year huge leap. But it'd be wrong to underplay the benefit of targeted boxes versus an ever moving target. The latest, greatest hardware in these case will never be ideally used. It'll basically be current gen +1, and it'll only play the new, exciting technologies once it's become worn in and a little slow by the latest standards.