actually, it is more of an Internationalisation issue as capital letters in other languages often translate differently, plus older databases insisted on capitals,
It is also good practice, as it helps in finding fieldnames as opposed to variables if your fieldnames are always caps and your variables of mixed case.
Makes Sense, though I prefer to have my SQL in CAPS and my fields in lowercase for pretty much the same reasons, but I can see how the language translation thing could be an issue.