I don't think pornhub is hosted in the US so those laws may not apply. They are based in Montreal, Canada I believe.
This is their 2257 page. I've bolded the relevant parts. Basically they circle around it by saying the content producers are responsible for collecting the 2257 paperwork, but that they expect producers to "verify the content", IE collect the relevant paperwork and verify that all models are over 18 years of age.
None of which has been done by people uploading the kind of videos we're discussing. Even if they don't fall under required compliance for 2257, they still need to verify that their "models" are over 18.
18 USC 2257 Statement: Pornhub.Com
Pornhub.com is not a producer (primary or secondary) of any and all of the content found on the website (Pornhub.com). With respect to the records as per 18 USC 2257 for any and all content found on this site, please kindly direct your request to the site for which the content was produced.
Pornhub.com is a video sharing site in which allows for the uploading, sharing and general viewing of various types of adult content and while Pornhub.com does the best it can with verifying compliance, it may not be 100% accurate.
Pornhub.com abides by the following procedures to ensure compliance:
Requiring all users to be 18 years of age to upload videos.
When uploading, user must verify the content; assure he/she is 18 years of age; certify that he/she keeps records of the models in the content and that they are over 18 years of age.
For further assistance and/or information in finding the content's originating site, please contact Pornhub.com compliance at [email protected]
Pornhub.com allows content to be flagged as inappropriate. Should any content be flagged as illegal, unlawful, harassing, harmful, offensive or various other reasons, Pornhub.com shall remove it from the site without delay.
Users of Pornhub.com who come across such content are urged to flag it as inappropriate by clicking 'Flag this video' link found below each video.
I would also speculate that even if PornHub doesn't require compliance, if the uploader is from the US, he's still liable in some fashion.