Interesting topic...!
Im not sure why they do use them - my guess would be:
People like Hermance etc are sponsored, so have to use the pedals. The trials-specific shoes they use also work ok with them.
Im not sure about Ashton etc... maybe theyre just used to those pedals from ages ago, when they were the only decent pedals available?
I can certainly say that, from my own experience, pinned pedals seems to offer much better grip, and also have larger platforms.
Many people say caged pedals work well with running-type trainers - but, i dont own any, so have never tried.
Definitely each to their own though! :P