Not quite either one -- it's technical enforcement by the TLD, but still done on a per-domain basis (this doesn't affect state/local .gov domains, or legislativ

Not quite either one -- it's technical enforcement by the TLD, but still done on a per-domain basis (this doesn't affect state/local .gov domains, or legislative/judicial .gov domains). The dotgov.gov program will forcibly preload new domains, but it's not feasible to just submit ".gov" to the preload list right now.