Default role vs, non-default role

I have two users, user1, and user 2 and both users have been granter ROLE1 and ROLE2. The only difference is that for user1 both ROLE1 and ROLE2 are default roles, and for user2 only ROLE2 as a default role. User2 reports that he cannot see some of the tables he can see when loged in as User1. Could that be because ROLE1 is not a default role for user2? Can someone explain the difference to me?