Perhaps the network effects of launch made it seem like there was really just one console to own this gen? Last gen you were missing something pretty significant without any one of the consoles--that's an intimidating choice and a lot to buy at once. Analysis paralysis can be a real problem.
Also--a certain amount of buyers would simply have been too young to buy a console. Wonder how that fits in? I can't imagine it's not related to gaming...as you've said, it's really not a great box for anything else, and unlike PS3 there's cheaper blue ray players now, like...the PS3.
I wonder if Indie games are a much bigger selling point to non-core gamers than people realize. Mobile has introduced them to smaller games and now they want a similar experience with nicer graphics on their TV? Any media capabilities the PS4 does have would help to justify the purchase some more.
I wonder if these are PC gamers who are now jumping into the console market either for the first time, or returning after a long absence.
These are folks who would be into the Indie scene, as well as wanting the most powerful console.
The last of us also may have had an influence as it is regarded as the best game of the generation and only playable on a Sony system. This may have pushed PC gamers into finally jumping into the playstation ecosystem.