The woman's speech was entirely appropriate for the circumstances. There are cases where imprecision is okay. This case is closer to what I'm getting at than the "where does a preposition go" case is. All I can say is that I've been in conversations with women like this - and I've heard conversations among men and women like this that were almost as funny as a "who's on first" routine. Sometimes that's okay. Sometimes it makes communication much less effective than it otherwise might have been.
"Grammar is not a magic salve for imprecision."
In fact, it's possible that using perfect grammar can impede effective communication. It's possible, but not so common as the case of using improper grammar, I think.
I'm reminded of the cases where I'm tutoring and I ask the students to explain a certain idea - and I'm sure to correct them and to coax them into repeating the explanation correctly - both so that they are using the correct terminology and so that they understand how to think about the problem correctly.
Learning grammar is a good thing. I'm glad - grateful even - for what grammar skills I possess. Sometimes precision in language is unnecessary - particularly in English with all its redundancy. And sometimes it's crucial.
If the primary purpose of communication is simply to identify one's self as part of a particular group, then the lack of precision is fine. In some cases, even a slight difference in vocabulary or sentence structure can alter the meaning dramatically.
I've seen cases where a very slight difference in wording on a briefing slide is the difference between a 3 month project and a 3 year project. Many times when I've been asked to review technical papers, I've had problems with people reporting what they think they did. I try to tell them, "No, that's not what you did. You're confusing the issue."
"Well, the customer knows what I did."
"But people other than your customer are going to read this and come to erroneous conclusions about what you did and what can be deduced from it."
and so on.
I'm not saying that one has to use perfect grammar all the time or that one has to forget whatever "natural" grammar one possesses. But expecting students to use only the grammar they learn at home (and that seems like the case you're making) makes about as much sense as expecting students to use only the math they learn at home.
