This is thoughtful design: Muji apparently released a flashlight that works with any combination of 2 AA and 2 AAA batteries, only more dimly with fewer batteries.
@acb I've always assumed that things that "require" X many batteries of X type are depending on all batteries to complete the circuit, not to mention the specific voltages of certain types of batteries. If that is true there's probably a way around it and that's probably what they did -- it's probably more components though and therefore more costly (although, to be fair, it's probably pennies on the dollar per hundred units or whatever).
@blake@acb I seem to recall reading some years ago that Microsoft had patented a *really simple* circuit to allow devices that run on one or more AA or AAA cells to auto-sense which way the batteries were inserted and flip polarity as necessary to operate. Can't imagine why this isn't in universal use already …