Why do Norwegians speak English very well?

I was in Norway this Autumn and I noticed that Norwegians speak English fluently, really fluently, more fluently then other Europeans (except the British, of course). I have some explanations for this.

Firstly, I figured out Norwegian is similar to English (they are both in the same language sub-category).
Secondly, Norwegian isn't a widespread language, so Norwegians have to learn other languages in order to speak with people outside Norway. For example for Spaniards their problem isn't as severe, because there's a lot of other Spanish speaking countries. Thirdly Norway is a highly developed country with a high education system. I believe that eduction level is correlated with English language level.

Inhabitants of the ROI (Republic of Ireland) speak English as good as the British.