okay, first of all what is the question. you say 'fashions' are you speaking in terms of genre? as in what is the difference between emo and indie? independent music is just like independent film, music that it is produced for less money, by smaller companies. as mainstream music didn't have any interest in some of these artists (nor did the artists have interest in the mainstream production companies), they were sort of solidified in their interests and thus certain styles emerged. for a long time indie music was placed in the category of alternative music but it basically split and formed its own genre around the time that alternative was occupying a major focus of the mainstream (with bands like nirvana). mainstream music didn't accept it or have much interest in it because, well we know that most people are stupid and looking for straight up good times/happy music. indie has a range of styles/attitudes emotional, quiet, soft, dreamy, melancholy, etc. obviously these don't go with mainstream music.
emo on the other hand, contrary to some peoples beliefs, did not come from indie music. it originally came from punk, a sort of artistic rendering of some of its styles (influences of course too). emocore bridged the transition from hardcore (similar to punk) to emo, because of the particular emotional expression that it gave.
but whats important is to understand that bands often utilize styles from more than one genre. modest mouse isn't just indie, it uses aspects of emo as well for sure.
if you have questions about this stuff a simple and easy to use source is www.allmusic.com
i didn't really understand your initial question so i have no clue if this answered any of what you were asking...
"if you stay ill totally put out." - markd13 in regards to my having had it with this site.