Unless your in a campaign where all characters roll stats in order, no swap outs or extra rolls. Regardless of 4D6 drop lowest or straight 3D6 rolls you can wind up with a poor CON stat, not many people do it this way but generally using this character generation system the DM is prepared for an important stat to be low by having certain magic items available to the player to make the early stages of the campaign survivable for them.
Edit: Also, at every table I've ever played at we roll for our HP, taking the average has been either house ruled out, one DM allowed it, but no one ever took it.
I understand some people house rule how ability scores are rolled or assigned, and house rule how to determine hit points on level up, that doesn't mean there needs to be errata to cover those groups. If you are already house ruling how to assign scores and limit h.p to only rolls, just house rule whatever you want for h.p on level up.