There probably is a group that will spend $500 just for that sports interactivity and the fact it's a game system/streaming box, probably that hypothetical sub-urban family. Question is how common is that REALLY? How many don't already, say, use iPads and the like if they cared that much and had that money to spend and really wanted to get it on the TV instead? And will it be hobbled by XBL fees or will they be looser this time around? Xbox's the top selling console yet not the top Netflix streaming service, while some people don't give a fuck and just pay the subscription anyway it does indicate enough people are probably catching on and continuation of that policy would probably see more people jump ship.
Mind, that's speculation and opinion to an extent too, but in addition to the Netflix bit cable users HAVE been dropping as Parapraxis noted, and the fact each system that was $100+ more (other than the PS2 relative to DC) has had trouble being adopted period does not bode well for XB1, especially when for the core audience it doesn't even have the factor of being strongest, even in an esoteric manner.
PS3 did seem to be rising at the same pace as 360 only to break around the Kinect's debut, but it would inarguably be behind if Japan hadn't more or less fully rejected the 360 unlike every other first world country. And admittedly the game thing IS more my own personal preference, there's exclusives to be had on XB1 but the PS3 tended to pick up what third party exclusives I cared about and Microsoft practically gave up publishing a large number of games part way through the generation so there simply wasn't much beyond Halo/Forza/Gears/Fable. Though if they stick with the support they showed at E3 I'd definitely need to get one, but I suspect they'll start strong then peter out. Poor indie support definitely isn't helping Microsoft though, and likely poor support for smaller developers/publishers period (360 print run limitations ARE a serious fiscal concern for multiplatforms as I recall.)
And I think the beating the PS3 took relative to the PS2's state IS interesting to note: they absolutely fell very hard, but even with that the PS3 is a reasonably close second if you factor out Japan, slightly ahead with Japan factored in, and Microsoft's going into the next generation without having accumulated the PS2's crazy numbers in a longer period of time. It makes me wonder if the PlayStation brand really DOES have enough momentum afterall, even if it wasn't enough to catapult to first place regardless of their missteps, and also if the Xbox really did establish a strong enough foothold anyway; it HAS been a long generation with many people growing up most of their teenage years with the Xbox, if not childhood period, it really may be comparable to what Sony had after the PS1 or PS2... though it could also matter as much as Sega's dominance for the early 16-bit years.
