PG's writing got the influence it has mainly because of his startup's success, and later YC's.
There are thousands of nerds with blogs musing about LISP and why nerds are the smartest kids in high school even though everyone thinks they're so lame; there's only one nerd that has such a blog along with a multi-million dollar startup buyout and multi-billion dollar startup accelerator.
If PG had never sold viaweb or started YC, no one would care about his blog.
You're right that money was a necessary ingredient, but it wasn't sufficient.
I didn't really care who he was or what his past achievements are, so at least in my case that proposition is false. I just liked his writing. It's probably impossible to know whether the audience resembled myself or your archetype, but it seems unlikely that hundreds of thousands of people heard about the Viaweb acquisition or about some rich Harvard graduate.
While the signals we look at to determine authority are varied and different for each person, style-of-writing is generally included in that list. Why would so much advice on etiquette and morality suggest ensuring one's written communications are of high quality?
I'll admit I didn't really read the links you posted but in looking over the first few paragraphs on http://www.paulgraham.com/taste.html he is clearing signaling his authority in how he name-drops MIT and talks about his MIT educator friend. (And I don't mean to imply there is anything wrong with that; writers are often advised to establish their qualifications early) I imagine the 18-year-old me would have felt confident about his essay simply from this reference.
Finally, the wannabe theory of thought leadership isn't a hard-and-fast rule. There are exceptions...
It has been quite the ride to see this random dude whose work I started reading become a global juggernaut.
He came to give a talk at my university when YC was just getting started, and while I was a junior there, about how we could start a startup, rather than going to big companies and working for others. This was very eye opening and exciting, and it was completely independent of his previous achievements - I had never heard of him before that talk, and I had never heard of his startup.
There's no contest that his blog was an instrument in his popularity; I am questioning that it was the main one.