They retracted that and apologized. It's unreasonable to just hold this over their heads, and in general use it to dismiss their entire project, which they have been working on for half a decade, mostly with no salary, because of one badly phrased sentence from one contributor which was then retracted.
I also think if you read the rest of what they're saying, it's probably is true that we will only get Linux GUIs which are competitive with Windows or Mac when people are willing to fund their professional development. OSS works exceptionally well for lower level components, or for components targeted at developers, because everyone involved benefits. For a professional developer a contribution acts as a good mechanism to raise your profile within the community and improve your ability to earn a decent salary elsewhere. For a company, running open source projects means they can solicit contributions and improve their profile; they contribute to other projects because it gives them a base to be able to build their products. We don't expect or find that OSS developers of high profile projects are starving in garrets, they are in fact leaders of their communities, highly prized and in-demand.
But these mechanisms do not have the same force when the consumer of the software is a general user, not a developer in the same field. i.e. when you're writing software in C++ which is then going to be used by graphic designers or artists, or by a casual user. In those case, the direct reputational benefits just aren't there, and that's why those sort of projects often struggle to take off. And on top of that those projects also involve a lot of painstaking and arguably boring work to get everything polished to a fine sheen. Krita for instance is excellent, but it has found a way to fund development through yearly crowdfunding. I think the same applies to Linux GUI's, that ultimately you need some pot of money able to support developers, which moves around according to the desires of informed consumers. In my opinion, that's what it will take for desktop Linux to become a serious mass market alternative to Mac and Windows.
My problem with their project funding argument is that I'm not an investor. An investor has lots of money, and so is more willing to accumulate risks for the payoff of creating a stable enterprise.
It's not rational for me as a consumer to fund such an unsure bet, especially when changing an operating system has lots of friction. I assume that the proposed talent of an individual investor is in the ability to sieve good from bad in a sea of maybe. But I also don't understand the market well enough to see how such an unproven bet might succeed in a very stale market dominated by arguably one entity (you can't really buy macOS) -- maybe two.
I'd also say that while software work is expensive and requires talented labor, and while operating system work takes an intense amount of effort, there's something to be said about the fact that Elementary OS could even build their OS to begin with. How did they do it? On the backs of billions of dollars of free labor. I can't imagine how it would be if the whole world hid their source code with proprietary-only software, and Elementary had to start from ground 0.
Your argument would make sense if it weren't pay what you like, with the option to pay zero, and the default option being less than the price of a sandwich.
You mention that investors have lots of money and are therefore able to take on risks. I suspect that nearly everyone who would consider downloading this operating system has a lot of money relative to the $5 suggested donation, and certainly relative to the $1 you could choose instead. And if you truly don't have that, then you can do $0 instead.
You can make the risk to yourself arbitrarily low, selecting whatever you think fits your profile of cost vs potential reward. That is their rational model.
http://m.slashdot.org/story/213469