I wonder if, rather than it being stock or fears of RDNA2, it's because Nvidia is rethinking their software given the stability problems of the 3080 and 3090 at ~2GHz?
Don't forget, the 3070 will be a cheaper card with cheaper VRMs and lower capacitor counts to save costs. If the extremely complex and expensive voltage regulation of the 3080 and 3090 weren't stable, how do you think the cheapo cut-down variants are going to fare without some serious driver work? It's too late to change the board design at this point, likely thousands of cards have already been manufactured with inadequate bypass capacitors on Nvidia's rushed and inadequately-tested reference design.