Correct, the crit tables are not open-ended.
And I forgot to mention something else in my previous post -- crits CAN receive adjustments -- for example, for melee, there is a Killing Strike and the Sacrifice Strike Combat Moves -- both of which allow for modifying the critical roll (the amount based upon the ranks in the combat style)
Plus there is always Ambush, which also allows for modifying the critical roll. Not to mention, the GM could always hand out weapons that improve the critical... hehe)
So, while attacks against super-large creatures means that you will not kill them easily, You can still kill them with criticals through means that allow for adjusting the critical....
And don't forget, that while attacks against SL get -30, "E" crits also get a +20, which means that the max possible normally is a 110.