What is the point of “likes” on Twitter?

The other day I had my most successful tweet yet. The hashtag “DullDownAMovie” had been trending, challenging users to change a movie title to make it boring, and I tweeted “Harry Potter and the Chamber of Commerce”. (Long ago, I volunteered at a Chamber of Commerce. Nice people, but boring work.)

The Twitterati agreed. I got a lot of re-tweets of that little quip. Personally, I didn’t even think it was the best suggestion I made. I preferred “Jane Got a Gnu”.

I also got a lot of “likes”, which brings me to the point of this post: what is the purpose of “likes” on Twitter? They seemingly don’t provide increased visibility at all, unlike re-tweets. (Quick summary for those unfamiliar with the medium: if a person retweets something, all their followers see it. If they like it, they don’t unless they make the additional effort to see their list of “likes”.)

Given that the platform exists to give people greater visibility, why is there a feature that does nothing to enhance visibility?

What's your stake in this, cowboy?