I don't really agree with this. Can you provide an example?
Because there are a million things you can do in objective c with the ui that are basically impossible to do with html5, and many many ui elements you can configure 100x faster in obj-c(they also run 100x faster). Hell even having a reasonable 2 column lay out is surprisingly difficult in html/css.
With obj c/native if you are unhappy with some functionality of the ui you can very easily break into open gl and do pretty much anything you can imagine if you have the talent.
As far as I can tell the only real advantages of using html5 is that you can hit many platforms poorly with one code base, and that maybe you don't really know how to program or understand object oriented programming.
I would not say speed of making a ui is a plus for html unless you are trying to hit a bunch of platforms poorly or do not know the native languages well.
As for error output - you just need to look at the logs in detail (and turn them up to trace) to get details for hard crashed.
What exactly would you do if the client came back to you and requested something titanium couldn't do?
When I was using it it had problems even moving to a page with a webview already loaded up to a webpage.
Have you built a project with a real native language for pay?