1. They’re trying to achieve mobile apps parity between different platforms
2. They don’t have enough programmers, and Google bought the shop they wanted to outsource to
3. Places and groups are going to have APIs and enhanced with more features soon
4. Single sign-on is going to be available on mobile platforms too, it’ll also be easier to use
5. iPad is not mobile, it is a computer

Seriously. Zuckerberg called iPad a computer.