It's a feature that - initially - Microsoft denied was possible on its next gen hardware, and something that a slightly bewildered Sony continues to claim is impossible on the PlayStation 4.
And yet, it's a feature that was demanded by many, who - when faced with the prospect of upgrading - would either have to keep two chunky consoles under their tellies, or witness a vast swathe of their game library being tossed abruptly into The Dark Pit of Hardware Obsolescence.
On the flip side of the coin, others have rolled their eyes, and complained that backwards compatibility is a failure of the release schedules. They say that publishers should be focusing on new titles which make the most of their hardware. And, in turn, make it worth their while to upgrade.
History records that the Xbox One got off to a rough start. General apathy with regard to the Kinect 2.0, PR howlers about the console needing to be always on and internet-connect, whispers about the PS4 being the more powerful machine, an absurd focus on the system being an all-in-one entertainment system rather than a games console... It all conspired to give the PS4 the public relations advantage.
With hindsight, there's not much difference between the two machines - and what difference their was (Kinect) actually served to make the Xbox One the more interesting system, in terms of doing something new. Unfortunately, it also made it the more expensive system; a strategic blunder that allowed Sony's PS4 to race into a seemingly unassailable lead.
Doubtless, Microsoft insisted on bundling the Kinect with every Xbox One sold to ensure that it had sufficient market coverage to make it worth releasing games for. Publishers still chose not to.
Rightly or wrongly, Xbox One owners wanted backwards compatibility, and Microsoft has delivered on that - when it initially thought it was impossible.
There will be many Xbox 360 owners who will now consider taking the next gen jump, so that they can continue playing their existing games.
Microsoft's announcement came out of nowhere, and came amid a strong E3 showing - one that focused almost exclusively on games... with a brief diversion into a demo of the intriguing Hololens. It was a PR masterstroke, and Sony suddenly looks to be on the backfoot, not least because so many of its PS4 announcements were for games that are a year or more away.
For whatever reason, the current generation of gaming has gotten off to a slow start. More than ever before, developers and publishers have kept a foot in the last generation. The charts and release schedules are still full of next gen remakes, old game anthologies, and games that have - presumably - been compromised on next gen, because they're cross-platform releases, developed alongside last-gen versions. When faced with all that, you can see why backwards compatibility might rankle with some.
But at the same time, it might just be the killer app which allows the Xbox One to close in on the PS4. The importance of the Xbox One's backwards compatibility is that it's a pretty profound demonstration of one thing - a thing that Microsoft has been doing quite brilliantly for the last year.
Microsoft is listening to its punters (and not through a creepy, always-on, camera thing that sits under your TV). The company is finally giving them what they want, not what it thinks they need.
FROM THE ARCHIVE:
XBOX ONE: THE RED WHIFF OF DEATH by Mr Biffo
XBOX KINECT 2.0: Requiem for a Dream
E3: SO THAT WAS THAT by Mr Biffo