No, but many of these may be used in much the same way as why Wikipedia links to tons of Twitter pages even though it's 'an aggregator of user-submitted content without much oversight' - the users themselves confer the the reliability. I wouldn't be surprised at all to see a pg comment used as a source in the Paul Graham article.

But that's a primary source. Generally, use of primary sources on Wikipedia should be limited because primary sources are easily subject to abuse. For instance, even something as simple as a quote from X that "Y is great" can be problematic. Is that what X really thinks? Is there a quote from somewhere where X says "Y is not great?" Was X really in a position to evaluate Y? Wikipedia articles should generally be based on reliable secondary and tertiary sources.

[https://en.wikipedia.org/wiki/Wikipedia:PRIMARY#Primary.2C_s...]

From your link: "Wikipedia articles should be based on reliable, published secondary sources and, to a lesser extent, on tertiary sources and primary sources."

That suggests that Wikipedia treats primary sources on par with tertiary.