I'd read that the current theory of how lightning rods protect a house, antenna tower, or other structure is by preventing lightning from striking -- that is, the sharply pointed rod lets charge dissipate from the structure, so that it doesn't build up a potential opposite that of the cloud and attract strikes.
I've also read (in older references, mostly) that lightning rods attract lightning and actually increase the risk of a strike, by offering a higher path for the stepped leader (and hence the main bolt) to ground.
I can easily see how either situation could be argued -- put up something to attract lightning and route the strike harmlessly to ground, or put up something that makes the strike less likely. It's been well known for a couple hundred years that lightning rods do appear to protect structures where they're correctly installed. What's the up to date theory on how?