"You do, and shall continue to in perpetuity, own its copy."
And therein lies the problem. The copy that you paid actual coins for can suddenly "vanish", apparently with no recompense.
"And even that copy's ink may fade, may its pages decompose, may its film color, may its bits rot."
May it be forcibly removed from existence after a couple of years as it was purchased to be a convenient tax write-off...?
"When does something become truly "owned"?"
It's not so much about ownership, I don't care who thinks they "own" something. It's about entering into a simple commercial contract. I provide money and they provide the content purchased. If they no longer have the rights, fine, don't sell any more. But leave alone the stuff that has already been purchased or people will turn to piracy - and when they realise how easy it is, where's the incentive to pay for the next thing that might suddenly vanish?
"If I were to say, "I made this", the only one to stop me would be other people to say I did not."
But did you make that?
"detetmine what you may do with what you "own""
I think you're getting hung up on the ownership and creation. Generally speaking, the object's creator doesn't have an awful lot of say in what you do with the object that I own. If it's a car, then clearly I cannot say that I made it, especially if there's a bloody great Citroën badge on the front. But I can drive it on the wrong side of the road, do 97 in a 30 zone, attempt handbrake turns on winding country roads, or just the old fashioned run people over. Citroën cannot stop me, and it isn't their job to, that's what the police are for.
If the physical thing is a DVD, well, okay, I'd like to see Warner telling me that it's just bad to pop the thing in the microwave. Or hang it from a tree to scare the predatory birds (that was the fate of many an AOL CD back in the day). Mount a clock mechanism in the middle? I own it so as long as I don't try to claim it as being my creation and/or make copies of the content (easier done with a CD than a car), pretty much everything else is my choice. Warner won't tell me I can only watch their not-for-children film after 9pm and Citroën won't tell me I cannot drive on Sundays...
"under a terms of service that were too long, didn't read"
Your words are yours, you retain all rights as the author. You just grant El Reg full worldwide rights to make copies (this is necessary in order to reproduce the comment in the comments section for other users to read).
"And alas, I own these words. Maybe."
And I own my drivel, except for the parts that were quoted for context. Though when you start discussing ownership and copyrights of comments on a forum, that way madness lies.
A far simpler way to look at the problem isn't "ownership", but simply if you pay money for something, what are the realistic expectations of how long you can enjoy the privilege of that purchase? If it's a digital copy of a film that is going to vanish soon, well that ought to be factored into the price. You aren't just buying the "content", you're also buying the promise of it's availability. And if that promise is broken.....