Ah, but you're forgetting about today's Hipster youth. They'd start wearing soda bottles ironically until it became an actual fashion.
Joking aside, I'll give you that media does tend stick with the celebrities, but remember that there wouldn't really be that many celebrities without media itself. Back in the day all they had were crude pencil sketches and testimonies. All anyone really got back then was a defining feature to distinguish them from a crowd. On top of that, there wasn't really a budget for customizing your clothes.
Another variable that I just thought of is that a lot of times these celebrities aren't the ones that are coming up with the trends, they're just popularizing them. Brad Pitt sees Average Joe wearing a green Tele-Tubee pinion and starts wearing one himself; the media sees it; throws Brad's picture everywhere showcasing the pinion; suddenly everyone in the world wants one.