Why does "gpg --export-secret-keys" ask for a password? What is it about the architecture of GPG that requires me to enter the password of the secret key when I export it with "gpg --export-secret-keys"?

I would expect that gpg can just copy the relevant part out of the keyring and dump it into a file, without a password prompt. After all, the exported form is still encrypted with my password.
man gpg...


  GnuPG  may ask you to enter the passphrase for the key.  This is required because the internal protection method of the secret key is different from the one specified by the OpenPGP protocol.


I guess that answers it.  Though if anybody knows more, feel free to share.