If you install both this AND the 'no music' version, you'll be able to use 1.7 features to swap the music in and out with other packs, or different music with L&T... Basically, it gives you more options about how you play your Minecraft.
Currently for Minecraft 1.7.4
If you want to play in Minecraft 1.6.4, download this version.
Unrelated to the pack, why has there recently been a My Little Pony trend? I honestly don't understand it...
Given that it started over a year and a half ago, I'm not sure you could call it "recent" anymore!
This stuff is all pretty off-topic, so I'll put it in a spoiler.
A "Brief" History of Bronies
A few days before the first episode of My Little Pony: Friendship is Magic aired in October 2010, an article was posted on cartoonbrew.com called The End of the Creator-Driven Era in TV Animation, which lamented on how cartoon greats such as Lauren Faust (creator of MLP:FiM) were now making cartoons for corporations rather than being able to make cartoons from themselves. 4chan's /co/ board found it and were intrigued, so the first episode was uploaded to YouTube after it aired, and the residents of /co/ found that it was actually good. The characters were interesting, the art style was great and the cliffhanger left them desperate to know what would happen next. ( is a pretty good approximation of that reaction if you want an idea.) These original fans became known as /co/lts ("colt" is the term for a young male pony).
Naturally, it spread from there as people recommended it to one another and almost everyone agreed that yes, it was great. It reached the infamous /b/, where the fans became known as /b/ronies, which is where the word "brony" originates. It was passed from forum to forum until a lot of websites had a group of pony fans on it.
But why people like it? It's a little hard to pinpoint. I'd say it's a combination of:
interaction between the creators and the fans (of which there is a lot!)
the irony of being a teenage/20-something y/o male who loves MLP
As I am a geckbro and not a brony, I can rate this on the actual textures and not how good MLP is: try adding more detail and shading. It's better than a simple pack, but certain textures are too simple.