BBM coming to Android & iOS

No doubt this is great news for many. Being able to connect with my parents over BBM will make it easy to keep in touch - affordably no less.

My question is this though, and I'm sure it's been answered in detail before, however, not everyone is doing it.

Does it help companies gain marketshare by expanding their services to multiple platforms in an attempt to give those users a look at the greenery on the other side of the fence? Or is it just about generating volume for that particular service?

Google has provided its services on iOS in a stunning manner, and with BB pushing BB10 to iOS and Android. How will they benefit most? Why isn't Microsoft getting Office on other platforms?

Cheers. It's going to be an exciting summer :)