Right but that was the AI being lucky. Everytime I've had them at my gates with a spy (gates open) they never rush it and 99% of the time will just waste time opening up holes in the walls which just gives me loads of time to organize my troops. What they should be doing is charging the gate before I can get all my troops into position. This is the tactic I normally use when siegeing and its very fail safe, because once you take the walls they can't use their towers to shoot at you and their moral takes a dump.

Can't say I've ever seen the AI use the "gates open, spy" technique with any common sence.