Didn't bother to read the entire thread , but anyway here's my :

1) Bugs get found when the software gets maltreated. Testers do a lot of things, but generally have enough knowledge and decency not to do that. Casual consumers & buggers have not.
2) The CA teams are not in the position say "here's the deal, we iron everything out and whatever it takes... so be it: quit nagging us!" because they'd be outta work the instant they say it.
3) On to pathfinding: well, based on my experience with RTW...
a) There appears to be a certain center within a unit, which is used to determine the general direction a unit has to go to... (forward, turning etc.);
b) However especially with large units: they don't fit in the smaller streets, or on walls, or in siege towers or between trees -> some of the unit gets stuck making the general calculations based on the unit center pretty worthless since the center isn't anymore where the unit itself is;
c) Buildings & trees count as obstacles (obviously), but hills on which buildings are built only partially count as such (that's why those ridiculous fences and stuff is place around them... makes it slightly less odd);
d) Those public gardens etc. count as obstacles as well, however a tree standing pressumably on the other side of the road, in engine terms is in fact part of the obstacle. May have been done with the idea "the garden is always to be surrounded by other buildings & this saves PC performance" in mind, may be not... whatever that's the case;
e) Units which are grouped are programmed to stay in formation; and to do that there's this "group center" simply the idea behind the unit center is being applied to multiple units as one unit of it's own.

Hopes this clears things up. At least thread's