>all it takes for an attacker to overcome the scheme is to replace your private keys with theirs -- or to patch a JMP for every do_license_check() call in the binary. It's fundamentally an approach that is always hackable.

That might be true in theory, but is non-trivial in practice. The code responsible for license verification is often obfuscated and tied to critical functionality, so you can't do a simple find and replace.