Good catch.I generally like what you've written there, but I have one little nit to pick, if I may. In saying that Paul here isn't listing things that apply to all Christians, you point out that he doesn't list murder or adultery. But you neglect that he does list not being covetous (I Tim 3:3), which is another of the Big 10. That doesn't negate the point that not all Christians are, e.g. apt to teach, but it does weaken the argument that nothing in this list is a addressing sins. (or, more specifically, that "he wouldn’t have to say anything about any activity that no Christian ought to be doing," because apparently, he did.)
Between you and me, I'd say that sandwiched between "not a brawler" and "rules well his own house" I can almost see the wheels turning in Paul's head as he switches gears from 'things that affect the man's relationships with others' to 'things actually under the man's jurisdiction' to the most intimate, internal problem: pride. If you're not coveting other people's stuff, you get into less brawls, and really you should be minding your own business anyway, which we can now talk about (rule your own house, manage your own children, and keep a lid on your pride if you're doing it well).
So in other words, I'm content that my argument based on the main thrust of Paul's argument is still solid, and I'm not sure (very personal, just my opinion) Paul was even thinking of covetousness in the 'commandment' sense there anyway, just thinking of regular sort of day-to-day 'misdemeanor' covetousness....
However, if I were in a hostile situation, and somebody thought they had just scored a major point by pointing that out, I would just quickly concede the point. Makes you look reasonable. And I tend to favor big picture, "what's the big idea" arguments anyway, as I find that most people don't have the attention span to follow long, convoluted, detailed presentations, and more importantly, the kind of guy that's going to make this connection and think that therefore this passage prohibits polygamy, therefore the whole bible prohibits polygamy, therefore God hates polygamy, etc, is not the kind of guy I should have been talking with in the first place anyway.
That's a real peek-behind-the-curtain kind of explanation (might have too much coffee circulating...), but it's a long way of saying your are absolutely right but I'm probably not going to change the webpage.