When it comes to the device's global search feature, Roku is the developer, period. Google is only pushing this because they know they have market/end-user leverage, not because it's inherently better for the user. And even if it is, that's for Roku's product managers to decide.

Your airplane engine analogy doesn't really work; Roku doesn't want to modify the YouTube app; this is purely Roku's own global search feature. Yes, it will aggregate results from the YT app, but Roku doesn't want to modify that data source. Further, the Rolls->Boeing/Airbus relationship is more like a vendor->purchaser arrangement, which is nothing like the Roku->Google relationship here.