"it was never highlighted to me that my log book needed to be updated"
In what way would you wish it to be "highlighted"? Try complying with the law by at least reading the instructions and you'll notice that any amendments etc are to be immediately notified to DVLA. Apart from that, they can't guess when you may switch addresses, can they?
It's no defence, either, for you to tell the authorities that you were 50 miles away etc. Just how many others have access to your car? Sounds to me like you're trying to wriggle out of this by acting dumb. Maybe you are?