The delete function did not exist back then. This is probably why they added it. You may have, especially during times of heavy traffic on the Bitcoin blockchain, seen block explorer info relating to as yet unconfirmed transactions, mentioning that the transaction is still living on a fork, and is not on the canonical chain. With bitcoin this can take hours when the transaction load is heavy.

Steemit added the delete function, and you can see, by actually looking at my transaction record on steemd, that when I delete a comment, you can no longer retrieve it. That's because it has been purged from the block in the confirmation process.