I wouldn't call them "popular" outside of Europe, just as most wouldn't. This is from early 2013. It echoes that belief.
http://www.fightsaga.com/Press-Rele...litschko-What-place-will-they-hold-in-history
I would disagree with that journalist specifically stating Eastern Europe though as even in Western Europe they're rather well known. They're certainly not household names in America, not like Tyson, Foreman, even Lewis (a Brit). America is still very much the mecca of boxing and that's just the way it is. It's unfortunate.