Here I was drafting a reply to theGreg from way back in the thread, and look what's happened in the meantime... goodness.
Anyway, leaving my intended post aside in order to jump into the thread where it stands now...
This is back to whether buggy-whip manufacturers can make money in the current technological age.
Buggy whips may not be the best analogy here, since the market for buggy whips literally disappeared due to technological changes in society. However, the market for media is arguably bigger than ever, which is one of the good things about the new digital world we live in. There are more opportunities and options for content creators than ever before, this is absolutely true.
The "buggy whip" that is in most jeopardy is high-end professional content, which as others have pointed out, only comes from a front-loaded high-priced investment of a lot of time and talent. Nobody will ever make that investment only to give it away for free and hope they get some donations. Without a reliable revenue stream to support such a risky undertaking, then yes, that industry will die out.
And thus it may well be that tv networks and movie studios will eventually go away. There may be a future where "media" is nothing but garage bands and youtube webcam videos, supported solely by donations because that's all they need to keep making them. However, since all of us DiF panelists make our livings in the buggy whip industry, you can maybe see why we're not excited about that prospect. 
I'll say this though - at the current state of things, the pay-model is still a far better bet than the donation-model, and the obvious example is Down In Front. Here at DiF we make content available for free on a weekly basis, and only ask (gently) for donations in return. Only Teague knows the dollar figures, but I'm gonna go out on a limb and guess there hasn't been a huge fiscal return on our three years of effort.
And that's fine, none of us does DiF to make money, nor do we expect to. But you should note that every one of us abandons DiF on any given week if there's a paying job available instead.
Even with its damn-near-nothing production overhead, it costs every single one of us something to make DiF every week. Even if it's mostly just time and gas money, that's not nothing.
Now I'll go out on a further limb and bet that if we changed to a paid model, we'd lose most of our listeners... and make a lot more money. If we switched to a ten-dollar-a-month-all-you-can-eat subscription model, and thus immediately reduced our listener base to a total of seventeen people... DiF would be making more money than it does now via unlimited availability and a donation model.
And although you pointed out some cases where donation models are successful, those remain the exception and not the rule. Most internet "we made a thing, now give us money if you liked it!" models are just like DiF - unprofitable.
Regardless of whether it's buggy whips or cars or Cloud Atlas or strawberry smoothies: if a thing is available for free, it has no value. We choose to make DiF free because what the hell, we don't care. But if you insist on removing the value from things that were intended to have it, you are removing the market incentive to make those things. You may not miss buggy whips, but you might miss (name of favorite tv show or movie) when it stops being worth making.
EDIT: Posted before I saw Teague's post, to which I will only say, wow. 