I wonder if research supports this? I.E. How do most people select their running shoes? By what a friend is wearing and recommends? By seeing what's on more people's feet? By what the kid at the running shoe store hocks? (Although at many major sporting goods stores now it is help yourself style.)
I seem to remember reading once that women are notably un-loyal in their allegiance to a brand, and more willing to try on several shoes for the look, or the feel, and also have several brands.
And of course we've all see the person with an adidas shirt, nike shoes, and puma socks.
Don't get me wrong, look, feel and fashion are important. But current trends are always influenced by the highest regarded in their field. Also certainly in sport there is "association with the best". If you look at the fashion industry most new trends are not modelled by the top models but by no names who
Nike signed up the Tiger Woods, Serena Williams to improve the brand association, not to sell golf equipment. Nike sign up runners with significant careers not because people will know their name, but so people in the know in that sport can see what the elites are doing and add credibility, brand image saturation and elite association. Shops, fans and will tend to recommend what the top athletes are wearing, people tend to shop for an image they have seen in a positive light and that has a wider know-on effect to the wider fashion of the sport. It's less direct than the Tiger Woods effect on the brand but it is important for sales of specific brands of shoes.
It's a similar reason why Nike swamped their athletes with fairly uniform neon colour shoes in the last Olympics. People take notice and copy.
A good explanation of how it works is done by Michael Johnson in this link on how kinesio tape became so widely used after 2008 when no-name athletes in the game started using it at the Olympics:
http://www.youtube.com/watch?v=6NKHJP7nFqoSadly the video missed the funny moment Jonathan Edwards referring to Paula Radcliffe's technical explanation of how it works says something like "why don't athletes just pinch their bum hole like we used to to get going? I assume you two did it as well?"