Swords used to (e.g. in 1.2.5) break blocks faster than hand. This only worked on blocks that could be harvested without a tool, and still caused 2 points of damage to the sword (as was normal for breaking a block with the wrong tool).
This no longer happens.
Since it wasn't mentioned in any changelog, I assume this is a bug, and not an intentional change.
Re-post of MC-16712 to get a moderator's attention.
Works as intended.