Think of it like in English. Man - men .... in swedish, man - män ... they are almost pronounced the same as in English. Many irregular english nouns (mouse - mice, or mus - möss) are similar in this way.
No, the man is mannen but the men has an on the end and the a changes!
ShayneSund, that's interesting. My friend from Finland remarked how tasteless it was to be served coffee in a paper cup in New York. She would have liked it in an attractive ceramic cup.