I can't tell if Rhodes creates 100% native apps or some kind of web/native hybrids, but it doesn't like it uses Apple's iOS SDK. RubyMotion lets you use the same APIs and classes as normal Objective-C apps, so all existing literature is totally useable.

And something I didn't mention in the tutorial: you can even use existing Objective-C frameworks and code in RubyMotion apps using CocoaPods[1].

[1]: http://cocoapods.org/