I don't actually have a clue when my road tax is due. Honestly. The good old disc was a reminder. In France you had to have a little square notice on your windscreen, too - this told everyone that you had insurance and reminded you when it was due to be renewed.
I could end up as someone who hasn't paid their road tax. I hope they post me a reminder - but doesn't that cost at least as much as issuing the disc? If they do it of course. 'If it ain't broke, don't fix it.'