I'm sure it also has to do with what country you were raised in, your exposure to media etc, your educational and support system, your level of motivation and dedication, and your aptitude. I taught English for three years in a foreign country to many smart people who struggled to learn the language. Although English is apparently not difficult for you, the claim that "English really isn't that hard" is clearly untrue for a great many learners. (Also there are a few minor errors in the above post ;))

As with anything, it depends. It's never seemed hard to me and I'm sure we can all agree that it's among the easier languages for people to learn. At least people coming from indoeuropean languages.

As for errors, I've noticed that spending time in the US and using colloquial English a lot, has wreaked havoc on my English grammar. Or maybe it's the distance from schooling that did it.