While I know that using a VPN has helped people getting their accounts back, who have been banned in the past.
I have to agree that what camelot10 is saying could be true and is already in place presently?
I recently took one of my laptops on a trip, far into a different region (16hours far) and used a hardline local ISP, and I didn't have a single locked/email/query.
My accounts were logged off during the flight and maybe a total of 30 hours before I started them up.
So I believe there could also be a time checking mechanism in place.
If you suddenly (YES a couple of hours is suddenly) jump from US -> Europe.
I would assume you are more likely to get flagged?
I have no proof but Blizzard could realistically be using "timer" and "hardware ID" checker along with the already known about IP checker.