The ability to recognize talented programmers and programs is pretty rare. This is why software projects with founders that can write usually succeed, because the responsibility of selling good code usually falls on the programmer (think Linux, Arc, Rails, etc).
Having the ability to see good code allows an investor to find the hidden gems-- excellent programs that no one knows about because they aren't promoted. I'd be willing to bet that there is a goldmine of ideas implemented in already existing code, just waiting to be discovered.
First, the projects you mentioned are great projects, but they're not something an angel investor would be interested in.
Second, most startups - or at least web startups - do not fail for lack of technical expertise. The product might be an unusable mess, or it might solve entirely the wrong problem, or it might be marketed in completely the wrong way, or there might simply not be enough demand for it. I'm sure there are cases where a startup fails for technical reasons, but I'm willing to bet real money that in the vast majority of cases investors and founders don't say "man, if only the programmers were a tiny bit better, we could've made it". (even when they do say it, chances are that wasn't the real problem)
You're correct, they're most definitely not projects that an investor would invest in. However, if I am going to invest in someone, I want to know they can code. I want to look at programs they wrote while they were in college, or working a job. If I see a novel solution, my confidence in my investee goes way up.
Tons of people have great ideas, but their success is going to be determined by how well they can code. When you say that startups don't fail because of a lack of technical expertise, you're right in a limited sense. Startups of decent calibur will not fail because the founders don't know closures, continuations, design patterns, etc; they'll still be able to build products. They just wont have the vision to know the full range of products they are capable of building. If that's the case, you'll only last as long as it takes for a better hacker to enter the market. Experts Exchange being overtaken by Stack Overflow is a perfect example. Same idea, but because actual hackers are running Stack Overflow, it's trouncing Experts Exchange, with no signs of slowing down.
What makes you think Stack Overflow has any technical advantage over Experts Exchange? And, what makes you think their growth rates are at all correlated?
As far as I can tell Stack Overflow is a perfect example of a site where technical talent is almost irrelevant. Just like this site. We're not here because this site is written in Arc. We're here because of the community.
If not technical in terms of CPU cycles, technical in terms of design. For one, I don't have to scroll all the way to the bottom of Stack Overflow to see the answers to a question. Stack Overflow also loads far faster, and has unobtrusive ads. These are things that hackers understand are important, and the suits have a difficult time understanding.
I think you're still missing tsally's point. He pointed out those projects because they required the original implementer to advocate them. His point was not that they would make good investments, but that they probably would not succeed on technical merit alone; they required someone who understand their technical contribution to advertise them to others.
I think your second point is off, too. Your argument is that startups usually fail for non-technical reasons, and I agree. But that's what tsally was trying to say: it's a rare person who can smell-out good technical work, understand it, and realize it's contribution. This is the sort of person you'd want to have as an adviser when it comes time to determine a business model or how to advertise.
Having the ability to see good code allows an investor to find the hidden gems-- excellent programs that no one knows about because they aren't promoted. I'd be willing to bet that there is a goldmine of ideas implemented in already existing code, just waiting to be discovered.