Metal (steel) roofs last as long or longer than asphalt. They are considerably lighter than asphalt roofs. They cost more though, which is why most people use asphalt shingles.
They are fairly common on some older (i.e. late 1800's early 1900's) houses because of their lighter weight. Also, I don't think they had asphalt shingles back then. They called them 'Tin' roofs. I always consdiered them inferior to asphalt roofs because they were on old farm houses and such.
Now, they are the latest rage. Copper roofs (which are metal) last about 300 years, but are very expensive. Most people use asphalt because its cheap and you can get 'south of the border' cheap labor to have them installed.
Regards,
Malta