In the arcades it was nearly always the other way around.
Really? Arcade games tend to be harder in the US.
For example, The Konami beatemups were edited so that some games had time-limit/health-meters (Crime Fighters) or health pick-ups were removed entirely (X-men)
This was mostly limited to beatemups though.
7th Saga for SNES had the stats tweaked with by Enix USA to make the game much more difficult than Elnard for the Super Famicom. After a while I grew to like the challenge, but compared to my playthrough of the import it was insanely difficult. My first playthrough I got stuck in the final world map area and couldn't even beat a random encounter to gain levels. Had to restart the entire game and ended up beating it with careful planning.
Funny thing about that.
What Enix did was A) make level-ups require more experience* and B) lessen the stat increases from level-ups.
Aside from making the game noticeably more difficult, it massively increased the possibility of ruining your progress.
In 7th Saga you choose from 7 heroes. They're all after these runes (which are attained through quests and stuff). It's not uncommon for the other 6 heroes to fight you and steal your runes if you're defeated. The other heroes level-up alongside you, but they receive the full Japanese-version stat bonuses. Thus, the more you level, the more of an advantage they'll gain. You could end up facing an impossible fight.
Then there's the giant middle-finger that is the final world. If your level is too low, you won't even be able to win the random battles!
*IIRC.
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Astro Boy Omega Factor US also received a difficulty-bump. Easy is Japan's normal, normal is Japan's hard, etc.