SATA tops out at 6Gb/s. One 7200 rpm spindle might not be able to saturate that, but a RAID array could, and any decent, single SSD would trivially saturate it.

So, for the kind of use case where you need to move lots of data, very quickly, eSATA may not be better :)

Well yeah, but a single ssd wouldn't hold lots of data, and for the use case described, I assume its a spinning rust drive. Also you wouldn't run a large raid array over a single sata bus, at the very least you'd use SAS and get multiple channels in one cable.

Edit: The g-raid mentioned looks like a 2x spinning array, so well within the limits of a single sata III bus.

esata is less ubiquitous than both USB and Thunderbolt (and firewire before it). External ports have never been standard on any macs and I don't ever remember them being standard on any of the HP machines we used (the majority of big budget editorial, i.e. feature films, tv, and commercials, are cut on macs, although fx leans heavily toward Windows and Linux). We use to install esata ports on some of our machine room systems, as the speed difference was definitely useful. I wish esata would have become more common but at the moment Thunderbolt makes it unnecessary (and USB3 seems to have stifled it's standard adoption across non-Apple systems).

Also, aside from the G-Raid, we also use 1 and 2tb SSD's (more for portability than the extra speed).