That all has to do with personnel there as well though.
Man Utd were extremely solid when they had Ferdinand at his prime and a Vidic who wasn't injured every couple of months. You can't expect someone like Jonny Evans to match them at their prime. At full back they again had better personnel like Evra at his peak and Neville and all, now a declining Evra and Rafael will never be as good as guys like them.
Arsenal the same, Adams and Campbell are of a different class to guys like Djourou and Vermaelen, Cole as well is much better.
Chelsea happen to have a clown in David Luiz at the back as well and a declining Terry. You can't expect a clown like him to be too good.
I don't think there's anything wrong with their defences, it's just they need better players there as opposed to the current inexperienced or declining guys they have there.
I think your post might suggest otherwise!