They're not irrelevant. Modern desktop spinning disk can hit transfer
rates from the platter well over 100MB/s, at least for sequ3ential
reads. Enterprise drives are often in the 300MB/s range. USB2.0 is
limited to a theoretical 60MB/s, but as in practical terms rarely
achieves more than about half that. Also I/O to the cache onboard the
drives can happen faster than that. So USB 2.0 really is a bottle
neck when performing bulk (sequential) I/O to a disk drive. For
random I/O, it makes little difference.
Now as to whether or not USB 3.0 is *really* ten times faster is a
different question (sure, the interface is ~10 times faster), but
there's no doubt that things like backups to an external drive can run
considerably faster with a USB 3.0 connection in many cases. Backups
are a major use case for external drives, so sequential performance
OTOH, the practical difference between SATA 1/2/3 and USB 3.0 is
fairly minor. OTTH, the difference between SATA 1 and SATA 3 is only
a factor of four, and SATA 1 is 150MB/s anyway, far faster than USB
2.0 (and SATA tends to use more of its theoretical bandwidth).
Likewise the fastest PATA (133MB/s) interfaces have not been too far
off keeping up with desktop drives until recently.
In a sense the practical difference between PATA-133, SATA-1/2/3 and
USB 3.0 are modest, but USB 2.0 (or say PATA-33) is actually