Yes, these companies seem far along. But do keep in mind that this is somewhat of a biased sample -- the dozen or so companies that "launch" on HN months before demo day are likely to be the companies that are the most far along.

There are ~100 other companies in the current batch [1] that haven't launched. I imagine many of those companies are not nearly as far along as the ones mentioned in this article, and some are still pivoting / navigating the idea maze.

That said, it does seem like in the most recent batches, YC companies get to demo day with significantly more traction than the early YC companies. I wonder to what extent that's because YC's reputation has gotten better over time (thus self selecting for startups with traction) or because it's gotten easier/cheaper/faster for startups to build a product and gain traction.

[1] I don't know the exact number of companies in the current batch. Last batch had 124 companies so using that as a proxy http://blog.ycombinator.com/yc-summer-2017-stats/