> zero reason why my browser should need to ever [...] use the accelerometer/gyro
It might not be a good reason, but I made a game a while back that used tilt input instead of arrow keys on mobile: http://nfriedly.github.io/space-jump/
A bit related, do ad companies use the tilt/gyro to guess if someone is actually looking at the video? It seems they could adjust payout based on if there was an actual view, or at least get some metrics on which ads people actually pay attention to.
