What is the language that you write in that doesn't "wrap another language"? I always find it amazing that it's possible to get programmers to argue against not just some specific abstraction, but abstraction as a general principle. What do you think programming is exactly, if not layers and layers of abstractions?
[edit: that's not to say I think the MobiRuby syntax is looking very good at the moment, but don't toss the baby with the bathwater]
It's not the wrapping of the language that is the issue. Unless you're writing bytecode by hand, every programer deals with some abstraction.
The issue is wrapping a language with a higher level abstraction, but then proceeding to use your abstraction with a framework designed for the lower language. In the case of the post, the author mentions using MacRuby/mRuby to Objective-C, but then proceeding to use it with Cocoa, which is really designed specifically for Objective-C. Using it with Ruby just ends up being awkward and unwieldy.
[edit: that's not to say I think the MobiRuby syntax is looking very good at the moment, but don't toss the baby with the bathwater]