Exactly! There should of course be no penalty for anyone attacking without a DoW. Quite the opposite should of course be the case. If you DoW, wait a few a days, and then attack you've lost the element of surprise - which was one of the key elements of the blitzkrieg (having your enemy standing baffled, while you drive past him, surround him, cut off his supply, and watch him stumble in panic into your mob-up groups clearing up 'behind' the front).
The only 'real' DoW's were probably that of the Allied on Germany in 1939 (after Poland), and that of Germany on the US (another testimony to Hitler's brilliant strategic mind ... let's declare war on the country with largest potential war machine - that's MUST be a good idea). - And as history showed none of these DoWs ended up being really smart moves (well, not for France and Germany anyway...). (Yeeeees, I know the the Allied didn't have much of a choice, and yeeeees the US would probably have entered the war against Germany not too long after that anyway, but I am CERTAIN that you get my point).
Anyway, the point is, actual DoWing is pointless!