they changed the type of model they used. Before, stock weapons were on v_models (viewmodels). Now, they're changed to c_models, which use the actual world model for the player's hands (which means they had to change the viewmodels to accomodate with the world model). C_models are kind of like a combination of v_models and w_models (world models, aka what you see on other people).
This also seems to have changed LOD (level of detail) on the models (because c_models have the highest polycount, which is why the textures have changed).