Thanks for letting us know about the change. I'm thinking that it might also have to do with giving users a small grace period where they are able to edit or delete their post/comment before it is recorded on the blockchain - because once it's on the blockchain, it's there forever! Even if it's edited after this point, anyone can use a block explorer to go back and see the original content, but this is different if the content is stored locally on a Steemit server for a few minutes before it is transferred to the Steem blockchain.