This actually makes sense; the porn industry has much higher earnings per user and hence a much greater loss due to lower conversion for those who don't have Flash installed. So for them, it's a "my hair is on fire" kind of thing. Whereas for Youtube et al., it's a nice-to-have.
Unless you hypothise that porn users not having flash installed is somehow a larger percentage compared to average web user not having flash installed?!
This is by far the largest reason for the delay. If you watch some youtube videos on your work computer, no big deal. But if you need to jack off at work, you had better use your own phone if you care about keeping your job at all.
I can't recall which article mentioned that this industry was very welcoming to new opportunities and features (one example was having seekable thumbnails).