"If you seek
service in a country that is not the country of purchase, you will comply with all applicable export laws
and regulations and be responsible for all custom duties, V.A.T. and other associated taxes and charges.
For international service, Apple may repair or exchange defective products and parts with comparable
products and parts that comply with local standards."
Those are the conditions on seeking warranty in other countries. So it means they give you warranty, but with those conditions.
Of course if you're in the middle of Africa that is going to be a problem... but not in most EU contries or American countries (US, Canada, Mexico, etc)
Found on
http://www.apple.com/legal/warranty/ (hardware warranty pdf)