Singing Artists

I've always wondered why some singers can sing their song in English very clearly, yet when they speak the language, they speak it with a foreign accent?

A classic example of this is when you listen to the Eurovision Song Contest and listen to all of the singers who are from foreign lands, some of the contestants sing the song so clearly in English, but when they have been interviewed afterwards, I've noticed that they speak with an accent. The group Abba is a good example of the type of singers I speak of, their English is so clear when sung, however, they speak with a Swedish accent which isn't detected in the songs they sing.

My guess is that singing is sustained and consists of fewer words than speaking. Also, singing involves a set of lyrics that the speaker does not need to come up with "on the fly"; thus, it's easier to focus on pronunciation.

I disagree. I can hear a slight Swedish accent in ABBA's singing, as minor as it is.