This is all pretty hand-wavy, but I think the idea is you are creating a wide open market wrapped up in a protocol, in such a way that the network effect becomes your advantage.
I believe the economic model is such that buyers reward nodes that are closer to where the content is being accessed most. I'm not positive, but I'm hoping the protocol actual distributes / moves content accordingly. If so, then you suddenly have something pretty neat, in that you incentivize providers to pop up where they are needed most, across country borders and at cut-throat rates.
Yes, this happens to some extent with CDNs now, but imagine anybody being able to be a CloudFront provider and being able to charge for storage at the same terms as everyone else and I think that is getting closer to what Filecoin is trying to do. (though I fully admit I may be totally wrong given that a lot of these details haven't been worked out yet)
To put it in more concrete terms, when I lived in Rwanda one big problem is that within the country the network is great, they have quite a bit of fiber and very developed mobile networks. But their connection to the outside internet is terrible, they have two pipes coming in and neither is reliable. So there would be great benefits to having local CDNs there, and Facebook and Google do but others don't because it just isn't worth it. You could see something like Filecoin being the economic incentive for someone local to provide that service and greatly increase the speed of internet access for everyone in the country.