You didn't even try the link and therefore misleading people into thinking that the post is in any way private, which it isn't.
You do NOT have to login into Google+ to read the post.
You do NOT have to login into Google+ to read the post.
I did try the link, it did demand that I login. I did not login, and it did not show me the content.
I resent such accusations, and suggest you make sure you are in full possession of facts before you do so.
Then again, I only access my gmail from it's own dedicated VM and noscript prevents GoogleApis and Analytics by default.
Do you think it possible that Google is requiring you to log in because it can identify you via typical tracking mechanisms?
I have better things to do than play "hunt the foible" on Google.
If Google knows you have an account because of tracking devices, they require you to log in because you are more salable.
If you're anonymous, you're more salable if they just show you the content.
In so far as I recall, originally G+ wouldn't show content without javascript turned on - i.e. the price of content was to allow Google to track you more closely.
To circumvent, you can put your browser into Private or Incognito browsing, and you can then read the post w/o logging in. (Which also logs you out of HN, so you can't comment or vote.)
So, for any of the HN audience with G+ accounts but who don't surf "logged in", a login is required unless the user takes extra steps (EDIT: such as incognito or child comment's noscript approach).