I agree with the comments by @Justin Morgan in that this really isn't very necessary.
The interface has been designed to highlight questions that have been deleted differently as well as including a note that it is deleted. The designers would have hoped that this state for a question would lead people not to think that they could vote on these items. The action is not going to happen very often because it is designed well...and if you do happen to click to vote without realising you get a message saying that the post is deleted and likely you release that it makes perfect sense.
I'm going to have a guess (ignoring laziness as an option here) that it really isn't worth the effort of putting more logic into displaying arrows when the interface has already been designed to reduce this behaviour...and in fact not seeing arrows may well add confusion to an interface that is already very consistent.