The offline bit wasn't disregarded, as soon as Google asked for it to be removed it was done so. As for the adverts it's hard to apply the correct ones if Google is blocking Microsoft from serving the correct ones. Google are still getting ad revenue from the ads Microsoft has implemented themselves with the metadata they can get access to. Microsoft seem more than willing to get this sorted but Google are the ones here being difficult.
It was disregarded, it's part of the Term Youtube publish , if someone at MSFT included it in the app someone was sleeping at the wheel and thinking they could get away with it.
It's business, Apple was similarly dickish to Google about Maps (heck look at how MSFT treats its partners to see dickish), it's not uncommon and end users can still access the service in the end.
No doubt but without the official one working then users have to find alternatives such as MetroTube and thus Google lose out on ad revenue.
Google probably earn more money on customers getting fed up with WP8 environments than some trickles ad revenues from people with WP8 devices.