In case it's not obvious from the juxtaposition of our two posts, I completely agree.

Having "tech famous" people on HN is great not because they're tech famous, but because they can provide the sorts of information that made them tech famous (as in, they're smart / knowledgeable). It's not important that they're famous, it's important that they can often provide insight into what we're talking about, because they were / are involved.

Reddit AMAs, when they're about a specific person (as opposed to a profession) seem to mostly be "You're awesome, I just wanted to ask, how did you get so awesome?" and variants.