[lemming]

I don't think it's that, it's more this:

Since higher protein intakes seem to have no negative effects in healthy people, one may want to err toward the higher amounts.

I haven't seen anything over 3.3g/kg recommended anywhere, and most people seem to recommend 1.4-2g/kg as a good baseline amount. The ISSN recommends this (see here: http://stevenlow.org/issn-position-statements-protein-and-ex...), however the ISSN does recommend higher amounts when losing weight:

Higher protein intakes (2.3–3.1 g/kg/d) may be needed to maximize the retention of lean body mass in resistance-trained subjects during hypocaloric periods.

Of course, none of this is required to get fit - you don't need to do the optimal thing to get a basic result. But you'll definitely gain lean mass faster if you do follow this. Those recommendations for weight gain (say 2g/kg with a caloric surplus) is easy to achieve with no supplementation and normal food, at least for an omnivore - vegans may have to work harder to get there.