Generally, even the most staunch libertarians are okay with such things because the payments and relationships are voluntary, issues like monopoly and free will notwithstanding.
But Twitter, FaceBook and even Google demand a form of somewhat involuntarily payment: time and attention. For some people, mainly the lucrative few who subsidize everyone else, time is much more scarce than money. These virtual "time-pennies" are sliced away in such negligible chunks that lead us to think we're not getting ripped off, but it's siphoning away an economic scarcity nonetheless, and everyone who participates in social media or any ad-supported services (which is asymptotically approaching everyone) pays the tax.
That's what Twitter's new rules really come down to: they couldn't give two figs about ensuring a consistent experience. It's an unsubtle smokescreen for "don't you dare interfere with our ads; that's our bread and butter you're f&*king with." It wouldn't surprise me if after locking down the client apps, they begin an aggressive cat-and-mouse game with ad-block plugins.
Is there anything wrong with any of this? Not inherently. But I'd much rather pay into a semi-socialist freemium service than one where my precious attention is sold to the highest bidder. (Dear App.net: go free-for-most with a paid tier, and you just might take over the world.)
I don't think App.net offering a paid tier would protect them from making the same mistakes as Twitter, Facebook, and Google down the road. If they grow to the size of any of those companies, they'd be susceptible to the same forces and temptations that are driving Twitter down its current path.
A privately owned company that provides services subsidized by one group of customers to others for free isn't "socialist" in any meaningful sense. It's still privately owned, it's still driven by profit, there's still money changing hands. It's funded by capitalists who put money in with the hope of seeing a return on their investment. Etc.
It's not impossible to imagine a "socialist Twitter," but that would involve something like it being operated as a venture owned cooperatively by the people who work there (http://en.wikipedia.org/wiki/Worker_cooperative), or as a wholly or partly nationalized enterprise, kind of like how the old Bell System worked from the 1930s until the 1980s.
Which is not a bad thing! I'm not saying that Twitter employees should run up the red flag and seize control of the means of production. I'm just saying that Twitter is a business, which is to say that it's an enterprise designed to enrich those who set it up. The fact that currently the easiest way to make that happen is to let some people use it free is tangential to that.
You are also repeating the last part of my post!
DejaNews was a company that held the most comprehensive archive of discussions on Usenet (http://en.wikipedia.org/wiki/Usenet) in the world at that time. Usenet was where public discussions happened online before Web forums, so that database represented an important chunk of early Internet history.
Deja had hoped to turn that database into a monetizable resource, but the bursting of the dot-com bubble ended that dream, and people started worrying that when Deja folded its Usenet archive might be lost forever. So Google stepped in and bought Deja to ensure that its archives would be held by someone who hadn't been crushed by the market collapse. Deja's archives eventually formed the basis of the product that became Google Groups.
There wasn't a lot of business logic to the acquisition; Usenet had been in decline for years by the time Deja sank, so if Google was only interested in a discussion product the Usenet archive wasn't a must-have. Buying Deja was more about saving a key piece of Net history (and putting it under the Google logo) than it was about financial prudence.
Of course, all this was in 2001, before Google went public. Private companies can make charitable gestures like this much more easily than public ones can.