In order to use WP8-specific features, developers will need to use a new development model. This is more friction for developers when compared to using comparable new features in iOS or Android, where the development model is unchanged, but new APIs are utilized.
One can only imagine the sorts of bureaucratic infighting within Microsoft as various development tool factions seek to discard the work of factions falling out of favor. In contrast consider how long Apple stuck by Objective-C as its chief development framework.