7% is a psychological number and a pretty high one. It's simple, if the yield is higher it means Italy has to pay more "intrest" on it's debt, and thus more cash to the banks it owes money to. This decreases the likelyhood that it can pay them off, and increases likelyhood of default. If it defaults, it can't pay the banks, and they run out of cash to lend to others (other countries, businesses etc) and this starts another credit crunch and cripples economies as they can't operate without borrowing a bit of cash here and there. So, approaching 7% increases fear in people that a default will happen, and with it a credit crunch, and with it a recession. Mainly, the "7%" is talked about because it's a psychological number.
The volumes in France vs Italy aren't that indicative in general, but there are some reasons. For one, France is the most exposed to Greek debt right now and an increase in Italy 10yr yields is indicative of market sentiment towards Greece to some extent, and in general to the whole Euro crisis. I believe France is also a big lender to Italy and that is another reason. Also, the two ETFs are different and the French one in general (afaik) has a little more volume than the Italian one. Volume increases on good news as well as bad news, so that's no surprise.