- Founded a successful web apps company back in the 1990s when that wasn't common, and sold it to Yahoo
- Founded Y Combinator to advise and invest in startups
- Smart investor with substantial success and track record (Dropbox, AirBnB, etc)
In other words, he's earned a reputation for doing some very smart things, and documenting them in clear, easily understood language, over the past 20 years.
I'm not being a mirer or a nuthugger here. I participate in HN because it benefits me and I learn useful things amidst the noise. (And of course pg started this site too.)