The only item I agree with is the last item: Objective-C is a nebulous term because it's so intrinsically tied to Apple and Cocoa/UIKit. The syntax? You pick it up within a week. Message passing versus method invocation? An important, but subtle distinction.

So what makes Obj-C hard? For me, it was Apple's gigantic MVC-style framework. Rewiring my brain to grok Obj-C was nothing compared to grokking Foundation Kit, UIKit and AppKit. Growing up with C++, C# and Java, you get used to a particular way of doing thing. APIs are designed and interacted with in a certain way. Apple's API feel completely different. From building strings and making network connections to working with images and animations. Apple's version just feels different.