[chromacity]

I'm not sure if this is what you mean by "distribution", but I think Instagram won by being content-consumption-centric. People who used Flickr were mostly other photographers. People on Instagram are mostly your customers: people planning their own weddings, moms with newborn children, etc. It's basically a marketing platform, so it's a no-brainer for current or aspiring pros.

It sucks for passionate hobbyists, but photography is first and foremost an industry.