Actually, there is a difference between the two. I have two .308win rifles with target chambers that won't even begin to chamber a 7.62x51 round. I also have a HK91 that will blow primers out of their pockets and create an unsafe condition if you try to shoot .308win ammo in it. However, I have two m14/M1a rifles that seem to be comfortable shooting either ammo.
But yes, the Russians are playing catch-up. There are many American rifles (even .308/7.62 caliber) that will still outshoot their newest offering.
There is an unspoken reason, too. In time of ‘war’, ol’ Josef comes across some left behind, or battle-strewn NATO rounds. Jackpot!