"The purpose of a system is what it does"

By this metric, HN is not a business promotion platform.

It's a promotion platform for a specific way of conducting business, and for the liberation of these businesses from democratic oversight (if not the other way around). And in that perspective, that's politics.

I probably don't disagree with that.

However, that doesn't equate to what I believe was being implied: HN as a business promotional tool specifically for YCombinator.