The included manual & cabling
The functional difference between Seagate's eSATA and the company's older external drives is that the new model lacks Firewire and USB connectivity. It is this lack of Firewire and USB options that we might change if we had the chance.
To be sure, this drive's strength is its exceptionally fast performance. But external drives typically have another strength that makes them valuable: portability. To migrate Seagate's external drive to another PC easily, that PC must have an eSATA connection (which does NOT mean a regular SATA connector).
Frankly, motherboards that come with an external SATA connection are still fairly rare. This leaves the user who lacks an external SATA connector with two options: either migrate the included eSATA card along with the drive, or open the PC case and plug the drive into a free eSATA connector if one is available. Both of these options require opening up the PC and fiddling with it, which kind of negates the value of having a mobile external drive in the first place.
Of course, you could argue that a media professional is probably going to have these bases covered and will have the newest PC equipment at their disposal, but that's a bit of a rationalization. The long and short of it is that if the drive has to be moved to another PC, there's probably going to have to be some prior planning to get it to work, whereas USB and Firewire drives can travel between PCs very easily.
