Umm. Not sure what copy of the BRB you are reading. Mine says that Chariots perform Sweep Attacks, not Vector Strikes. The Necron codex also calls them Sweep Attacks. There is no mention of Vector Strike.
Of course, being a Chariot, the Overlord can Sweep Attack a unit, shoot it with the Command Barge and then assault with D6 HoW attacks.
"Fetch me another plaything. This one seems to have broken." -Urien Rakarth
Space Marine- "This planet is ours, witch."
Eldar- "No ... This planet is theirs ..."