I think the point is being missed....

One of the beauties of SCSI is it's EXTERNAL capabilities as a extremely fast interface. Take a unit like the EXP400 for X series IBM servers. 14 10K 74G SCSI drives in an expansion chassis. That's connected externally to a controller in the X series. Expanding the storage capability of the server by 14 drives at no performance hit

You attach a USB2 hard drive to that server, it's not going to compete with the SCSI interface (or even the IDE!)...

eSata is an offshoot of standard SATA allowing for LOW-COST scenarios and performance that matches INTERNAL controllers. eSATA theoretically gives outstanding throughput and brings it up to almost SCSI arena for EXTERNAL devices. This means low cost SANs can built using eSATA instead of SCSI... and benefit from storage capacity of SATA