I always wonder that given our duty to pray for the souls of those in purgatory, perhaps All Souls or the 'Commemoration of the Faithful Departed' (as it is officially titled), should perhaps be a day of obligation - especially as since there is a plenary indulgence that can be gained for the those very souls we pray for.
Although Holy Mother the Church does grant some flexibility in so much as every day until the 8th - the indulgence can be gained by saying prayers for the departed in a cemetery, upon the usual conditions: communion within a couple of days, confession within a week, and finally prayers for the Holy Father.
But given the congregation at Birmingham today, I need not worry to much! An obligation to attend Mass was not required for the large turnout at The Oratory - was both impressive and reassuring!