"I mean even tree collisions were removed and these were in the original?"
The original trees on this huge map brought the sim to its knees. The only way they could put enough trees on the map was licencing "SpeedTree". Unfortunately putting a collision model on the "SpeedTree" program would also bring the sim to its knees.
There is very little I like about "SpeedTree", and hopefully the development will be able optimize them or replace them with something better. You can't see the forests for the trees
making visual navigation difficult in COD.