The difference is you have to be following the sender, otherwise they can't DM you. Though it's pretty silly and Twitter did remove the restriction recently, te

The difference is you have to be following the sender, otherwise they can't DM you. Though it's pretty silly and Twitter did remove the restriction recently, temporarily. They'll need to work on it if they want to make DMs more useful. Anyway, I do actually think this is useful functionality. It can only be sent from another GMail user, so Google will quickly know if it's being abused.