A fellow who calls himself Andrea Ritsu has an interesting post entitled “Magical Record,” on the subject of magical girl anime. This is supposed to be the first in a series, but he’s only posted one so far that I can find, on the subject of exactly what is and is not a magical girl show.
Although he spends several paragraphs discussing irrelevancies mirroring his personal preoccupation, it is a good discussion overall. He does a fine job distinguishing the magical girl per se from stories that happen to feature girls who use magic. It’s worth reading.