The ARRL originally required that electronic log files were named
<callsign>.LOG. This goes back prior to the Cabrillo days. When the
Cabrillo spec was being developed, I suggested to author N5KO that a better
naming requirement be developed. Trey declined to do this, wanting to
maintain convention for the ARRL's submittal process.
So that's what NA did. Funny, that many of the other programs decided to
do their own thing. Prior to the introduction of the log submittal robot,
we used to see all kinds of names for Cabrillo files - .CAB, .TXT, etc.
The problem with always naming the Cabrillo file as <callsign>.LOG is that
its altogether too easy to overwrite a file you wanted to keep, or to
submit the wrong file. Suppose you're getting ready to submit your CW and
SSB logs - you generate the CW Cabrillo file, then the SSB one. The SSB
version just overwrote the CW one. You have to actually open the file to
tell which is which.
As K9TM pointed out, about 2-1/2 years ago we changed NA to name the
Cabrillo file as <filename>.LOG. True, you have to rename the file before
you e-mail it, but the process seems to cause less headaches. We did not
do this in a vacuum - we polled the users on this reflector and there was a
pretty clear mandate to change.