This is true!
Most of the models in europe do not have an airco system and have bumper covers (up to the end of "97) without grills for the radiator. If an after market airco is installed, a slot has to be trimmed out of the bumper cover for sufficient air-flow.
The later models (since 9-"97) have different bumpers (2 types) with an integrated grill. This grill is either covered with a closed or grated (black) panel.
I can imagine that the completely closed bumper covers do not provide enough air-flow for the "aircod" US-models.
with a minor 600+k