Let me lay a little groundwork here. Journalism is a trade with no agreed-upon professional standards, so this is a tad haphazard, but here a few broadly accepted principles when somebody says something that is obviously butchered:
1. You don't qualify it with "sic." Even the AP Stylebook says that.
2. Mangled quotes typically are repaired by paraphrasing instead of quoting directly:
Sen. Burns said that he would never sell out his country or state. "Ain't no way I'm gonna do it," he said.
3. Some reporters think it's OK to repair mangled utterances even in direct quotes. Others frown on that. Either way, your ear does an amazing job of editing speech even when you are trying to get it exactly. Just compare a written transcript with what you thought you heard sometime.
4. Mangled quotes may be preserved in certain instances:
A. When quoting exactly is particularly important, such as a response to a criminal allegation or formal charge, or when the quote may have been heard by large numbers of people.
B. When the mangled quote is unusally revealing or apt. No one would ever want to correct, "Say it ain't so, Joe." Which is why I left the ungrammatical "ain't" alone in Point 2 above. And "amprehension," as a combination, presumably, of "apprehension" and "comprehension," ain't that bad a word.
C. When the reporter wants to subtly convey the message that the speaker is ignorant and unlettered.
The theory behind those principles is that everybody misspeaks, so it isn't fair to single out a simple misstatement and showcase it in a newspaper story. So what was Gransbery thinking? I have a lot of respect for Jim, so I wouldn't accuse him of "C." Possibly, elements of A, B and C were involved in the decision to use the messed-up quote.
Was printing the error a good idea? I wouldn't have done it, but I'm feeling fairly obsolete these days.