Truly, we don't get where we get because of our capacity or our ability (in most cases). We get lucky, a lot, and we can't really change that.
Much of the remaining "luck" comes from our choices. Think of it this way: how many people choose to work a steady job for all of their life. They will never be a billionaire, regardless of how lucky they get, and so their contribution to the average is zero. Actually, I suspect this invalidates your math: more than 1 in 2 people have probability zero of being a billionaire simply by virtue of not taking the chance of being one, and therefore of the people who take the chance, the odds are significantly better than 0.0001%.
People who actually care about these odds (in the sense of betting on them) are founders and investors. Neither, in their decision making process, gets to (or wants to!) uniformly sample all companies.
PG's numbers are thus much more useful to anyone actually trying to make a decision about a pool of investments: assuming the distribution of YC startups is fixed over time, and you are someone like Start Fund who will bet on the pool (i.e. equivalent to a repeated uniform sampling in expected value), the 0.5% is actionable information and the 0.00006% is not.
For example, if the prior on "making a successful company" (defined however you want) were a vastly higher 40%, then I'd imagine a lot more laypeople would take the plunge. Reading sites like TechCrunch makes it seem to the layperson that building a successful company is much easier than it really is. So yes, knowing that "mega success" is a massive outlier (to the tune of 1:1,000,000) is indeed actionable information to a layperson thinking about starting a company without any additional evidence.
As the source article notes: The goal of the entrepreneur is to learn as much as they can, thereby increasing their own odds of success (or minimizing their odds of failure). Obviously, getting into YC massively improves your odds and would probably be a good decision! As a YC alum, my advise would jive with this observation. ;)
That depends on how, exactly, you define "luck". I posit that a lot of what people call "luck" can be manufactured, or at least cultivated through directed action.
Remember the article that showed up here a while back about "How to date a supermodel"? The premise was that if you want to date a supermodel, you have to move to a city where there are lots of supermodels, and hang out at the places where supermodels shop, work out, dine, etc., and you have to start conversations with supermodels, blah, blah..
So if one of you buddies shows up next year dating a supermodel, everybody is probably going to go "Dude, that's amazing, you are SO lucky!" And this will completely ignore the fact that he did a lot of things to create the opportunity.
It's SUCH a cliche, but I guess cliches exist for a reason, so I'll just come back to:
Luck = Preparation + Opportunity
Likewise, if you don't want to date anyone at all, you move to silicon valley and work on a startup!
(Kidding! sort of...)
To date one you would need to be compatible with her lifestyle. That means highly successful or at least part of a similar industry like fashion or music. It means that you have to be somebody that can be announced in gossip columns as dating her. It has to be a good career move for her.
Naomi Cambel once walked past me while I was hanging out backstage at New York fashion week. Even if I had said hi there are still significant reasons why I am not now dating her.
And so it is with startups. Pedigree matters, the pedigree of your investors matters. Press matters and is heavily influenced by your position in the network. People in the game are deciding who the winners and losers are. Public perception is influenced by that.