I don't see any reason why it should _not_ shell out to bash. TeX/LaTeX was developed in a UNIX environment, which has the explicit philosophy of "the tool box with lots of little tools which do whatever little they do extremely good".
The iOS Philosophy of "It has to be one binary app" resembles the philosophy of Windows Programs. Big single programs with lots of functionality unter one big GUI.
How can anyone really be suprised that one of the oldest and mightiest gods of one religion can not be coerced into the shrine of a completely different religion?
Personally, I'm in the camp of "rely on as little as you can". This includes not shelling out to bash unless you really really really can't achieve the same thing with a bit of more code. Apart from making the app less portable, more bug prone, less maintainable etc, it's just ugly.
How can anyone really be suprised that one of the oldest and mightiest gods of one religion can not be coerced into the shrine of a completely different religion?