My Little Pony: Friendship is Magic is the 4 Generation done by Hasbro. It's creator, Lauren Faust, who also created great shows like Foster's Home for Imaginary friends, and Powerpuff girls, wanted MLP to take a step away from being girly, and have a more of a family safe approach. Eventually, this caught on to other demographics, such as men and teens ranging from 15-30 years old. That's where it is most popular, although a lot of other people enjoy it too, girls included. Duh. XD
This group of people came to call themselves a brony, Bro+Pony = Brony. Some girls like to be called pegasisters, but there isn't a set term.
Why do we watch this show? There are several reasons, ranging from the good animation, that progressively get's better as the seasons go on; The multitude of references most kids won't understand; Great Voice actors/actresses (such as John D Lancing and Tara Strong, who also voices Timmy Turner in The Fairly Odd Parents, and Bubbles from The Power Puff Girls); Likable cast that has depth, great characterization, and who are easily relatable with. The list goes on, but those are the main reasons.
Go watch the show! - at least the first couple episodes (it doesn't grip many until the 5th or 6th) and see what you think! If you don't like it, well, now you know why these "Ponies" have gotten so popular. If you do end up liking it, then WELCOME TO THE HERD!
Here's the first episode in case you decide to watch it [link]
Alright, most people wouldn't read all of that. XD Thanks
The first season was definitely aimed more at girls, but in the second season, it is DEFINITELY not for little girls anymore. You also might be thinking about the shows from 1980 - 2006. Those were, well, Those were REALLY meant for little girls.