Sony has in fact made it very clear what their little "hi-res" decal entails: (
source)
同社が定義する「ハイレゾ製品」は、再生周波数帯域40kHz以上のモデルで、その中でも社内の聴感検査をパスしたモデルと定めている。
1. Frequency response goes above 40kHz (which is what I mean by "compliant" headphones, e.g. the MDR-1)
2. must pass an internal SQ evaluation (i.e. should audibly bear out the benefit of a source that's not just CD-quality)
Sony has always made it very clear that their hi-res == anything above CD-spec, they never promised more.
Since you doubted that Sony might have downsampled the output, I'm really just trying to point out that
A. according to Sony's internal standards they would not sell a product with downsampled playback as hi-res,
and that B, there's an interview online that says the headphone jack is putting out more than 20kHz.
You can argue all day about whether Sony really managed to pull it off, but I don't see anything outlandish with these claims at all. If you think it's a marketing ploy then I think you should ask yourself whether you should believe in the benefits of ANY hi-def audio spec.
But listen, you think what you wanna think, it's not like my pride is invested in hi-res audio one way or another. Even if you think it's all a marketing game, it's you who's the williing participant.