But why then did duolingo state e and ed were used to personal preference?

You only use ed before vowels, like wow we say "a" and "an".

Hi, I don't know if your question's been answered already, but when you see e (without an accent), it means 'and.' In contrast, è (with an accent) is the third person conjugated form of essere ('to be') in the present tense, meaning 'he/she/it is.'

As of my typing this in January 2014, Duo allows you to get away with typing e in place of è. However, you should use the accent mark appropriately, as explained above. Hope this helps!

E davanti consonanti,ed davanti a vocali. Esempio:Uomini e donne but Uomini ed animali