This is actually a fair and valid point. On all but the most delicately configured systems, the standard configuration of basically all SQL databases does not occlude committed data loss during power failure due to the hard disk's write cache. See for example http://www.postgresql.org/docs/8.3/static/wal-reliability.ht...:

    When the operating system sends a write request to the disk
    hardware, there is little it can do to make sure the data has
    arrived at a truly non-volatile storage area. Rather, it is the
    administrator's responsibility to be sure that all storage
    components ensure data integrity. Avoid disk controllers that have
    non-battery-backed write caches. At the drive level, disable
    write-back caching if the drive cannot guarantee the data will be
    written before shutdown.

Which almost nobody does, because performance falls through the floor unless you're pimping a $500 RAID card (don't even mention software RAID).

The SQLite documentation goes into further detail surrounding the atomicity of writing a single 512 byte sector during a power failure (on old drives, on 4096 byte drives, and on SSDs). Few people seem to account for any of this stuff, yet sleep soundly at night regardless.

Since it's impossible to completely avoid catastrophic hardware failure in the real world, obviously that can't be the threshold for durability. But losing data to anything short of hardware failure means you're non-durable. Software crashes can't lose data. Kernel panics can't lose data. Power outages can't lose data.

> Isn't that just a higher likelihood of "durability"?

It's much, much, much more likely to have a memory failure (a crash anywhere from thread to hardware) than a hard drive failure. I don't mind them claiming that as durability.