Is the out of sync effect influenced by signal strength?
This ought not to be the case but why is it often very different. Sometimes it is even correct!
Like all things digital, it seems to me that not enough research was done into this problem before rushing into production.
Surely all it would take is some form of sync signal encoded with the sound and referenced to the video. On decoding in the receiver variable delays could be introduced to pull it back together.

Feel free to develop this idea, I'll worry about royalties when you have made your first million!!!!