I think or KNOW that the general public has a much bigger picture of what a slice should be. But then again, the slice served at a restaurant is bigger. Also, sizes of ALL foods are way too much as we know. This seems large enough to me.
Of course the general public has a 'bigger picture' of what a serving should be. Everything is super sized and HUGE portions now a days! When you go to the fast food places and you can't even easily carry a large drink in one hand, people get the idea what that is what the size everything should be.
If they want bigger slices of cake, then fine they can order (and pay for) more cake, but it doesn't mean that you have to join the rest of the food industry and have a portion that is overly big.