Why is Ruby so special? How does it impact Mobile App Development? I don't quite understand how or why rails and ruby is relevant. I'm very new to understanding how and why Ruby is very relevant in Silicon Valley.

Ruby is a language. It is very much like other scripting languages such as Perl and Python. There is nothing that makes Ruby any more special than other similar languages: it is more of a personal preference (style) thing.

For me, Perl is a write-only language and I don't like trying to maintain projects written in it. Python is nice except for the whitespace thing (and a few other annoyances like lack of regular expressions built into the language). I think Ruby has nice features for what I need so I use it when I can.

In reality, what your team or current project decide as the language of choice will dictate what you use at the time. You best bet is to become good at adapting to new languages so you can understand each of their limitations when you do end up using them.