Re: the lack of trouble at the Checkatrade final, me and the missus were on a Metropolitan Line tube from Hillingdon, and it was about 50:50 Sky Blues and Oxford. Not a hint of trouble. Got a bit lary around some of the pubs out by Wembley Park tube station, but didn't see any trouble all day (all the Oxford fans were long gone by the time we had got out the ground).
However, this being my first time at the new Wembley, I have extreme doubts as to how crowd control would be managed if a sizeable group of fans were intent on causing trouble around the ground, on Wembley Way, or at the Stadium or Park stations.
My uncle is a Bradford fan, and he chose not to go to the playoff final because they were playing Millwall. Just picture what might have happened if they had lost.
On the rugby crowds side of things, I used to go to Leicester Tigers when I lived up that way, and the only time I saw any hint of trouble (other than on the pitch!) was at the big finals, when there was a glut of tickets, and non-rugby fans were able to get hold of them for a good day out. And why not (as Barry Norman would say)?
But at a big sporting venue, all beered-up in sight of the pitch, no segregation, they did not know how to behave, and thought they were at a football match. Thankfully, there were a lot of 40s-50s guys there who had been lock forwards, etc, and took them in hand, telling them in no uncertain terms to cut it out. Self-policing is something we could adopt in the round ball game, but some of the little scrotes these days think they're invincible.