My impression on the difficulty of games like those from the NES era (and those that try to be, like Mega Man 9 and the Bit.Trip series) is that they stress anticipation while modern games stress reaction and adaptability. For example, in most NES games you eventually train yourself to expect one of 2 things (sometimes even both) when you see a pit:
1. Something's going to jump out of it when you jump over it.
2. Something's going to swoop down at you from off-screen when you jump over the pit.
You train yourself to spot patterns and anticipate what the game's going to throw at you. If there is a pit, you edge close to the edge to see if something's going to jump out, and then you shoot while jumping to eliminate the air attack that's coming. In Bit.Trip Beat, often I can't see many of the bits as they fly at me, but because I've spotted a pattern to the bits I've hit so far I can anticipate where the new bits will land. Old games also had a habit of just being completely unfair, such as giving you 3 lives period and no continues in a long game with a fondness for instant death traps.
In modern games, developers try to introduce new skills in a gradual curve, so that as new challenges arise the players aren't completely blindsided because they have been trained to handle it. The challenges end up being a culmination of what they have already learned, with the added bonus of having the player adapt their skillset to match what the game is now throwing at them. But you are meant as a player to get through it within a handful of attempts. In an NES game, you might need to play the entire game several times before pure memorization allows you to anticipate what a challenge will throw at you through (for lack of a better term) "gamer muscle memory". We also have usually plentiful checkpoints and save systems to allow us to pummel a specific challenge until we get it without having to repeat the entire game.
In general, old games were hard because they were cheap, relying on traps; quick reaction times; and brutal punishment for failure. Memorization wasn't good game design back then and it hasn't gotten any better now. I find that in newer games, when I fail at a challenge it has more directly to do with my lack of skill.
EDIT: And as for the soundtrack question, I'd love to see more of them come to the U.S. as well because the import fees for them are ridiculous. It still makes absolutely no sense that Nintendo of America has never brought over the Mario Galaxy and Twilight Princess soundtracks to the U.S. Club Nintendo. The big work has already been done on them for localization, so what's the hold-up? Were envelopes and cards just that much bigger sellers?