Does iTunes balance transfers when you change country?
I opened my iTunes account in the US in 2009, and then moved back to Norway in 2010. After asking customer support, I learned that I needed to use up (most of) my remaining balance before I could change country, and I lost the remaining balance when doing the switch. (This was no great hardship to me. I had to use gift cards to pay when I was in the US, because my only credit cards were issued in Norway, so the balance was never very high to begin with.)

Of course, that was two and a half years ago, and procedures may have changed since then.