> Technically, "Anonymous Likes" aren't really susceptible to spamming
[Citation Needed]
Should content show up higher in Google Search Results, if it is more Liked? By whatever system of Likes you care to design... I say "yes."
That makes the "Anonymous Like" system a clear target for Search Engine Optimization.
People have to pay for ads. If it turns out that the Conversion numbers for a set of search words are lousy, then advertisers will give up on those words, and the price on those words will plummet. It's to Google's advantage to find GOOD ads, that users actually WANT to see. It's good for advertisers to only have their ads up if users WANT to see them. And it's good for users to only see ads that they WANT to see. The economy on ad words helps solve those problems.
For YouTube videos, Google knows how many people watch all the way through a video - which is one metric. They know how many times people start watching the video. They could know how many "Anonymous Likes" there are. And they can know how many +1s and Shares there are. The number of replays, too. How often people click on the video, when it shows up in search results.
Given all of that data, I assert that it's possible that Anonymous Likes have no technical value. The task: given all of the metrics, predict the likelihood that User B will enjoy watching a video. I think it's possible that Google / YouTube have determined that the number of Anonymous Likes has no statistical correlation to the likelihood that User B will enjoy watching the video. I think it's possible that the number of Anonymous Likes should have no bearing on the Rank of a video in Search Results.
Your assertion is that "The decision to eliminate 'Anonymous Likes' is not a result of technical needs". That's possible, but I think you're only speculating. Otherwise, [Citation Needed].
> it's a decision "from the above" to force a "more social" Google.
If I'm correct, that Anonymous Likes have no statistical correlation to whether User B will enjoy the video, then don't you think it's possible that having Google+ users, who are signed in, be able to +1 and Share a video might actually create BETTER RESULTS for users? Not just "more social," but more "ME" based on things I've liked, and based somewhat on the things the people in my Circles have liked?