I like that you respond to an "AI is too dead set on sieges" post and then an "AI doesn't stick it its sieges" post back to back.
Is there a way to perhaps, at appropriate or seemingly appropriate times, have the AI detach a minimal siege force and then move the rest off? Bug or intended, they definitely take a TON of damage from attrition when over-sieging, and if they simply put the troops in a neighboring province that would make reinforcing reasonably simple (especially for a computer's reaction times) and possibly help them out a good deal.
Fort thing aside, because I don't think I see the relative stupidity others do (they just make a few sidesteps to get places) and they seem the same as always... the DOW thing is really bad. I think it's at least as bad, if not the worst, it's ever been. Could you possible add AT LEAST a check before the AI declares war that determines if they can potentially reach their wargoal without the other side having to make peace first? Augsburg conquest of Tirol doesn't work when Tirol and everything else nearby is occupied by France. The only way for Augsburg's AI to make any gains would be for Austria to end their other war... which means that Austria is now unsieged and can possibly wipe the floor with them. This is one I see all the time; I'll have French provinces sieged down, and then wimps will declare on the broken French nation, but they can't get any real warscore because France has no armies and I own all the land. As soon as I finally make peace, these wimps are as good as dead.
On a similar note to being able to occupy the wargoal, reaching it doesn't seem too great. It's rare, but I too have seen the Nation X declares on Y and then stays home phenomenon. I don't know if they're having access blocked they counted on or maybe their navy failed and I missed it, not sure, but it seems to happen rarely but enough to notice. Papal conquest of Provence is my favorite; it usually results in the Papacy losing Avignon.