My understanding of it is that Google are exercising item 8 in their terms of service:
Usage and Quotas. YouTube may, in its sole discretion, set a quota of operations on Your YouTube API usage. You shall not attempt to circumvent automated use-quota restrictions.
It does seem to me that companies should provide the same service to all users of any given API. If Microsoft started playing tit-for-tat by doing shenanigans like saying "HeapAlloc returns NULL always if the process is called 'chrome.exe'" the world would be a worse place.
I see... restriction via the API key.
The US does have anti-competitive laws that would prevent Google from offering Apple 1 deal and not MS the same. The only way Google is getting away w/ it right now is that the new YouTube app is Google's, not Apple. Google can just say, we haven't made the investment in making our own YouTube app for WP8 because there's so FEW users lol
And in NO way would degrading the OS for Chrome.exe be legal