Ask HN: Is it common for an HN user to be a CTO/VP/Director level employee?

It's probably about as common as being a CTO/VP/Director level employee within the general population. Most HN users are likely individual contributors; this is because most people are individual contributors.

(I did know one VP at Google who read HN. Only one, though.)

You can still be a CXX/Director and contribute, but I'll agree its more rare.

The HN crowd self selects to people deeply interested in tech. For instance, there's many VC's and founders lurking or public in the comments section. Never seen that anywhere else.

I wouldn't think about it much. The population on here is more likely to be VC/founder/VP than other internet forums but 95% of those people still aren't on HN. Too small sample population

Probably pretty common, I did/do. I know several other C-Level/Directors that do, but probably only in the tech/internet space.