Disabling autoplay on iOS is not unreasonable. I don't want autoplay anywhere, but I really would not expect opening a web page on my phone to start blaring random audio out the speakers. I wouldn't call that "sabotage", I'd call that "someone actually cares about what users expect". (That's leaving alone data concerns, especially with limited and expensive 3G data plans.)

Theres no reason this couldn't be a user permissions thing like the geolocation API's. If the user wants a particular page to have autoplay enabled, then the user should have the choice.

They could always allow you to mute sites by default. You see to be overly optimistic that they are doing it for the users good.

How is "mute by default" different from "no autoplay" except that when users actually hit play, it would just start somewhere in the middle? (That sounds like an even worse user experience.)

It would be "no autoplay by default" instead of "mute by default".

the difference is that in the "no autoplay ever" case I would be not able to enable it if I wanted. "No autoplay by default" is the reasonable initial setting, while still giving users a choice.

Settings -> Safari -> Audio -> On/Off, or with a permissions dialog

There is no good reason to have Audio off by default and have no way to turn it on for games.