EmojiOne came into smiley scene as an open source, free emoji pack. With time they have gone through a lot of changes. Both in terms of license and graphics. The emojis started looking more realistic and natural. As for changes with regard to the license, the author / team wanted to earn something from the project. I won't blame them. Other than SVG, PNGs are free even with their latest version. No one can put in a lot of work and give everything free. But, in the end, EmojiOne is no longer what it used to be.
Believe me, if you are trying to use it, and don't mind shelling out some money for your project, they are still a very good choice to you.
The latest news about EmojiOne is that they are coming up with version 4.0 on this August 21 st. Eagerly waiting for 4.0, and the license terms