The bigger reason to use RubyMotion is not a different syntax - you do end up using very similar code anyway, although lack of header files is a nice thing - but different tools. Objective-C is not the barrier. Xcode is.
After many attempts at getting started with Xcode and Objective-C had fizzled...it was an absolute joy trying RubyMotion and getting setup as an iOS Developer last night.
I can't wait to learn more, and it's wonderful being able to develop in Sublime, use RubyGems, Git, etc.