Every (or almost every) division had an artillery regiment in WW2. In all previous HoIs it was abstracted. Artillery brigade (visible as separate entity) symbolises strenghtened artillery for given division. We won't be seeing it in every combat unit that had an artillery regiment. That is the case with recon companies and such too.
Maciek
Exactly correct, I'm sure. Out of a division of about 10,000 soliders there will of course be small radio or signals groups which are too tiny to be mentioned in this game but present, historically.