I guess 500px doesn't care for it's community as much as they want you to believe.
I had an executive email me last month on my thoughts for improvements. I suggested the possibility of photographers having a little more control over pricing, since the prices they have set are a bit high. I guess the idea didn't fly.
Last night I saw another photographer post to Twitter about http://fineartamerica.com, so I checked it out. It looks pretty great, and I could keep my travelerspics.us domain. The yearly cost is less than half, and you have a big degree of control over the sales prices, which can be as low as almost half of what 500px sells for.
So I wrote back the exec at 500px, and here is a bit of the correspondence I received regarding switching. " If your main reason for buying a subscription for 500px is to sell Canvas Wall Art, then this might be a good move."
...duh. ...Why would anyone pay for a service to sell stuff, not be paying for that...