The Greeks would never use cheddar anyway (that's a lie actually as they use a cheese close to cheddar which is basically cheddar but it's the greek version (called kafelotiri, and mix it 50/50 with parmesan). The cypriots put potato in theirs too just for your edification. Also you tend to add breadcrums to the top when browning it off with the cheese. In fact it's all rather magic, and to get a good moussaka is very hard to find and most restaurants unfortunately do very generic and bland versions