A technical question: Why does a coinbase transaction put the public key itself in the scriptPubKey, while a regular transaction puts the public key hash (address) in the scriptPubKey? (And as a consequence, the scriptSig to redeem a coinbase transaction doesn't include the public key, unlike the scriptSig to redeem a regular transaction.)

Is there a motivation behind this, or is it an arbitrary implementation detail?

Reference: https://en.bitcoin.it/wiki/Script#Standard_Generation_Transaction_.28pay-to-pubkey.29