Epson won an ITC ruling some time ago that directly effects the ability for 3rd party inks to be sold in the USA. I'm not sure how MIS may be getting around this, but Epson already took Media Street to court. Therefore, InkjetMall only sells their inks as bulk systems with CIS, or large format printer carts, which were not effected by the ruling (though I hear one is still pending related to that too). Pre-filled desktop cartridges, which were a staple of their business, had to be dropped to avoid spending the rest of the decade in courts...
You can buy their bottles, and fill empty carts you can get from MIS, but a CIS is much less hassle.
Tyler