Not true. I've attempted Vault of Glass 3 times on normal mode and beat Vault of Glass 3 times on normal mode. Each time it was a group of 6 random people thrown together on one of the group finder websites. One time, two of the people were husband and wife but they had never played with anyone else in the group. I'm sure having a group you've played with before speeds things up but the only real requirement is access to voice chat, which Bungie has already said they are working on for match-made groups.