Moving to WebM may not save money for Apple. They gain money everytime someone pays MPEG LA for H.264 as they are one of the licensors. If H.264 loses widespread adoption Apple loses its share of the fees too.
It's hard to say whether Apple actually gains anything. For all we know, they might be happy to break even.
They pay for H.264 license to distribute their decoder, but collect royalty for their patents from every other codec vendor, device maker and commercial video distributor in the world.
Presuming Apple contributes a couple of patents to the pool, it doesn't seem likely that any income from MPEG LA would have any significance for them. Especially since they have to pay as a distributor of H.264 decoders anyway.