> so the reasons given by Google don't add up
They add up perfectly, though it may be inconvenient for WP users.
You CAN use youtube on WP using the mobile site. You just don't have a native app. They're not denying WP users or content creators anything except a little bit of convenience and battery life.
And as far financial or rational reasons - Microsoft is still extracting patent fees from Android handset makers. It makes a lot of financial sense to hurt them back - so when you come to the negotiation table, you have something to negotiate. Don't you think?