I don't understand it either. A Moggie is a Morris Minor, and always has been.
Must be a very local thing. I've never heard of a Morris Minor being called a Moggie, many other things, usually unprintable, but never a Moggie.
How do you define "very local"? I live on the South Coast, I seem to remember DaveW is somewhere in the frozen north!
I've met people all over the UK who use the term Moggie to refer to a Morris Minor. If I was telling someone, who didn't already know, that I drove a "Mog" I'm willing to bet a higher proportion of them would assume a Morris Minor than a Morgan.
~iw