The 3000 series will have built-in OC of up to 200MHz via Precision Boost (on decent premium X570 mobos) so that is exactly where the benefit of the higher TDP will play a role. The 3800X will allow a higher boost w/o manual OC over the 3700X.
AMD aren't complete retards. I believe that people who think they are clever cheapskates by buying a 3700X and hoping it will OC just as well as a 3800X are going to be in for a rude awakening.
It's not my money though so don't really care... just a friendly warning that AMD isn't arbitrarily putting these TDP limits as labels on their SKUs.
The 3700X will most likely have built-in auto-throttling to maintain its 65W target while the 3800X is free to run wild and suck up to 105W outta the wall. With that 65W limit you ain't going far if you attempt to OC...