Hey all!
The bulk of the movie simply
MUST feature Earthly Thor, otherwise...
1. Its a waste of the license. This is Marvel's 'Mighty Thor' - the fundamental basis of Marvel's Thor is that he is a fish out of water.
2. It does nothing to set up Thor on Earth for the eventual Avengers movie, and in fact actually hinders it.
3. Hollywood simply want to take the easy option and jump on the Lord of the Rings bandwagon with a 'generic' fantasy movie. Didn't work with Eragon...won't work here.
4. Asgardian Thor before his life as Don Blake was not a hero, nor was he a sympathetic character. He was a bully. No one will like that Thor, and if you don't use that Thor you take away the whole reason why he was sent to Earth in the first place!
5. (As chiefchirpa mentioned) Thor is less special when he is amongst other gods. If everyone has super-strength then whats so special about having super-strength!? You also lose a lot of the mystique of Asgard by revealing it all in the first movie.
6. Its disrespectful to the comic. Do we need a history lesson over what happens when you make a lot of changes from the comics? I'll tell you what happens - the movies SUCK! You would think after years of mistakes Hollywood might see a pattern emerging. I don't want Hollywood's hubris ruining Thor as well.
I defy anyone to come up with a rational argument as to why it should be Asgard only.