Some of us have no access to plus.google.com at work though.
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).