I don't know if this is what is going on:
[Note: the two documents below have been changed by Apple in late 2017 and no longer contain the information quoted.]
App Store [for iOS devices] Frequently Asked Questions (FAQ) - http://support.apple.com/kb/HT2001 when using iTunes --> "To change countries, scroll to the end of the iTunes Store home page and click the flag indicating the current country. To choose a different country, click the appropriate flag."
iOS: Changing the signed-in iTunes Store account - https://support.apple.com/HT204053 - Change your iTunes Store country: "Sign in to the account for the iTunes Store region you'd like to use. Tap Settings > iTunes & App Stores > Apple ID: > View Apple ID > Country/Region." (wording from old document; new document does not contain this information).