And yet, we happen to live in a world where practically no customer has the needed expertise to verify for themselves if the LED reflects the true state of the camera or not, and if they had it they'd not care any less. A world where corporations misuse technology to betray customer's confidence and break the law, and when those get caught, get away with no more than a slap in the hand (as in the VW emission control hack case).
So, what are you going to do about it? Throw a tantrum because you exist in Earth instead of Heaven, or work out a solution that you can implement yourself without need of consensus from the ignorant masses or permission from their corrupt leadership?
(Like you, I had always assumed that the power for the webcam was literally in series with the LED, so that disabling the LED would render the camera inoperable. That seemed like the obvious way to do it if you wanted to provide a truly reliable signal. But evidently that's not the case.)
If I were tasked with making a webcam circuit, I'd make sure the light and the sensor were always powered together. So I (naively) assumed that's how everyone would do it.
Of course, there are many cameras that do not even have an activity indiator (LED), e.g. stand-alone cameras, or simply your phone front and back camera. I find it a good habit to cover all cameras, regardless of wether they have an indicator.