Haniel_Adhar: It is actually the opposite.
NES games released in the US were magnitudes harder than the Japanese versions. Take Mad City/Bayou Billy for example. The Mad City JP version was way easier than the NES port, and the same with some of the Contra games.
The "Americans are stupid" theme is getting old. We are not as stupid as you guys think we are.
I also finished Bayou Billy on the console when I was a kid. Americans during the 80s and early 90s demanded harder games, and manufacturers took it too seriously at times. Friday the 13th and Jaws are perfect examples. I beat those two as well on the NES but had to leave the thing on for two weeks. Not easy games, but this is what we played.
Bloodlines is not a good game in my opinion. It's easy but also just not that interesting to me. Dracula X I think was a lot better. Harder because of all the timed jumps.
Thing is, with JRPGs it was often the opposite. The most famous example of this was Final Fantasy 4. The Japanese release was fairly difficult (though, I believe not as hard as the later 3D remake), but they thought the US, which had missed the previous two entries in the series, wouldn't be able to handle it. So, they made the game easier, dummied out many skills and items (if you hack them in, they're literally called "Dummy"; this may have been the origin of the term), and released the result in the US as "Final Fantasy 2" (skipping the numbers so that US players wouldn't wonder what happened to 2 and 3).
I could also mention that the US got a simplified RPG called "Final Fantasy Mystic Quest", while Japan instead got the more complex Final Fantasy 5 (my favorite game in the series, and I wish that game had originally seen US release, and that later FF games would have improved on it rather than taking an entirely different direction).
There's also a few examples where leveling up is faster in the US version than in the Japanese version. I believe Dragon Warrior 3 (NES) is one example of it, and I also heard that it happened with Super Hydlide (Hydlide 3 for the Sega Genesis).
As for (non-RPG) games being harder in the US, I've heard that's because of rentals. In Japan, video game rentals were illegal, but in the US they were legal, so they made the games harder so that they couldn't be beaten in a single rental.
Another thing: Rondo of Blood and Dracula X aren't the same thing. I haven't played either, but I've heard that Dracula X is the harder of the two games.
And that US Castlevania 3 (the one in this collection, actually) is harder than the Japanese one.
On the other hand, Japan got two versions of Castlevania 1: A disk version that has a save feature, and a later cartridge version that has an easy mode (that the easy mode in Bloodstained Classic Mode seems to be based off).