The eSATA is higher bandwidth and that means as TheKrell has posted the benefits of eSATA vs. USB2.0. eSATA provides for full functionality for at least 2 tuner DVR's that use the EHD as both recording and playback medium as with TiVo, just one example. It would not function so if it were based on a USB2.0 connection. I (others agree) that the reason Dish could never deliver on its promise of external HDD DVR functionality for the ViP 222 and ViP 222K is because USB2.0 was the only port provided for external HDD instead of including an eSATA port, as evey other maker of DVR of that time and a few years before had.
Further, the WD My DVR expander (the official external HDD endorsed by most MVPD's including Dish, DirecTV, TiVo, and more) has both USB2.0 (to support Dish) and eSATA (to support everyone else) ports. Dish could activate the eSATA for external HDD if it wanted to, but they may have other plans for the eSATA and may forever stick with USB2.0. Yes, it would be nice if one could transfer to the external HDD and watch a recording from the same external HDD at the same time. eSATA would provide the bandwidth for this to work without stressing resources.