Folks don't seem to be willing to "buy" GPUC in order to buy the cards. If they were, the market would right itself. What's the trade volume? Look at that, it'll tell you the story.
Also this: Mining GPUC to get a GPUC.. GPUC value goes down with BTC value.. this raises the electrical cost by a factor of 2.. so fewer people are interested in simply mining to get GPU's.
If more non miners bought GPUC through some method, and then purchased at the GPUC store, then you'd see a nice surge. Which goes back to.. the business frontend needing volume.
We could definitely see a number of changes to their storefront to make their business more sucessful. There are some critical errors they have not fixed yet.
For example most people will not be able to use the store as they do not know where to obtain GPUCoin. There is still not a single link on the entire store website that links to a page with general information about how people get GPUCoins. People are going to pay a little more just because of how inconvenient the entire process is. Search engines are not too helpful either.