When you measure 7.62x51 in CUP (50k) and 308 Win in PSI (60k), it is easy to think that the 308 Win is loaded to a higher pressure. You cannot reliably convert between the two scales, but both cartridges use the same load data from government and civilian sources so I am of the opinion that there is no functional pressure difference.
What 7.62x51 NATO spec ammo must do that 308 Win is not required to do is meet specific gas port pressure standards for use in machine guns and semi-automatic rifles. This is why you should not load just any 308 Win load in an M1A, AR-10 or 7.62 Garand. The same condition exists in 30-06, that there are loads that meet the specifications for use in the M1 Garand, and there are loads that do not. But no one is arguing that military 30-06 isn't spec'd to the same pressure as civilian 30-06.
But this myth will never die, at least not in my lifetime.
Jimro