again, I don't find the distinction useful as it is generally used among most readers. Precisely because it is applied to any comic that puts a big tear drop next to a character's head.
However, while I don't think it should mean "comics from Japan" either, I don't see your comparison valid. People who buy Japanese cars aren't typically doing so because of their interest in Japanese culture, or even in Japanese cars (beyond the fact that this particular model has some feature, usually cost or gas efficiency). Thus they have no reason to WANT to use a term for Japanese cars other than "Japanese cars."
Manga readers (however they use the term), on the other hand, are specifically trying to single a subset out, thus they need a term for that. There is generally some attempt to identify with Japanese culture, so it provides a need to call it by a name that is more authentic. For that reason alone I think you have a strong argument for rightfully calling "comics from Japan" by the term "manga" and not using other terms.
Now, when it comes down to it, it may be a slight misnomer to say I don't think it's a useful distinction, and I appreciate you calling that to my attention. There ARE a set of conventions (which DO typically include big eyes and small mouths, I don't think pointing that out is ignorant), but those conventions are often used in other forms as well. As a comparatist, I already find the borders between movements and style groupings much more hazy than your typical reader, and with manga I see that fuzzy area being much larger. The conventions also being used for many other styles. Most importantly, I don't find the grouping of conventions as nearly useful for predicting someone who is looking at the work from a scholarly standpoint will find items of use in a work. I think the content groupings of typical Japanese comics to be much more useful (magical girl, giant robot, etc), primarily because they compare more favorably with genre distinctions like science fiction or superhero.
In other words, I don't think the stylization alone (especially when most people I talk with define manga as anything with something approachign a specific line art style, executed well or poorly) is a good way to distinguish whether a comic is good or bad with it. [as an aside, I don't think that I've HAD a serious conversation about manga with you, Ookla, and I very much expect that you have something better to say about manga and what distinguishes it than this very limited approach that annoys me].
Perhaps the best answer is that I should simply narrow what I define as manga, but since I don't believe most of my audience makes that distinction, and I want to avoid too much of a technical nature, I decided to break that as a useful term for the purposes of my column. It is definitely not intended to reduce any subset of comics in terms of its contribution. I don't hate or like a poem just because it is a sonnet. So even if we take manga as a distinction, it doesn't determine what value it has.
Short form of what I just said: you're right, the easy definitions that people use for "manga" are not valid ones. And that's more or less what I'm countering with that statement, but since that's the usage I understand most to have, I've chosen not to use it as a term in my column. Is it poorly worded? Was that a poor choice on my part? Maybe to both. We shall see.