Truthfully, I agree with this new stance of theirs and believe it's always been the case, but there's no doubt that they're only adopting it now because it's become advantageous.
Sure. But there's a fair amount of US Copyright law that says this has never been the case. To test this hypothesis, upload a video to YouTube with music by Prince playing in the background.
Copyright law is more of an ideal, and if it had "never been the case", there wouldn't have been any content to DMCA off of YouTube in the first place. US copyright law is fighting the tide, not conveying a natural order.