The yanks liked the NES alot more because Nintendo marketed it and promoted it furiously in America. When first released the NES was promoted not as a Video Game system (which at the time, video games were seen as things of the past.........the gaming slump of the late 80's) but instead as an all round entertainment system (and was also called the AVS, Advanced Video System, then changed to NES before launch). It came with the lightgun, a copy of Duck Hunt, a copy of Hogans Alley and also a small robot toy called ROB who interacted with the games.
The NES was first launched in New York by Nintendo themselves, and sold 50'000 units in that area alone. Then Super Mario Bros came out and Nintendo decided that they needed to find another American owned company to distribute the NES. They chose Worlds Of Wonder, a company which had sold the most popular toy of the year called Teddy Ruxpin. Now because Nintendo had teamed up with such a huge company they were able to promote the NES is bigger retail stores like Toys R Us, and because it was being distributed by a company who created the highest selling toy it because an instant fascination.
Not to mention the fact that Super Mario Bros was a fantastic title, and people bought the system just to play that game.
Then later on when the NES was literally flying off the shelves Nintendo dropped Worlds Of Wonder and decided to distribute alone. One major reason why they could control such a huge grip on the market was because they would threaten large retail stores and say that they would cease all shipments of NES' to them if they changed their prices or distributed games that were not official condoned by Nintendo (alot of law suits came from this).
And that is also another reason why the NES was a far more popular system, every game had to obide by Nintendo's strict quality control/conduct measures, making sure that all of the game were of decent quality. They didn't want to end up like the Atari 2600 with a heap of games, and the majority of them incredibly shite.
And as you could probably realise by now, Nintendo still abides by this rule today. All games have to be passed by Nintendo and follow their guidelines.
So coupled with the fact that Nintendo marketed the NES perfectly, and they had some killer titles in their lineup they became a huge success in America. It was the first country outside of Japan where they wanted to market their technology, and they managed to do it.