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.
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.