i believe they do this for all of the above...
1) more direct airflow
2) ergonomics and noise control for the operator

yes it turns the truck into a floor sweeper and the radiator does catch alot of debris... but in that arguement i do believe these engineers are counting on the companies to keep thier floors clean and the operators part in doing thier daily checks and blowing off of the lifts before and/or after each shift.

Since the trucks designs have moved towards these directions the customer has to become more involved in daily mainteneance, unlike the old days when they could just wait for the tech to come out and service the truck like before.

the only problem with this is you have to rely on EVERY part of the equasion to work and unfortunatly we all know the customer/operator does not do thier daily checks as they should. So..... is the problem REALLY a design issue? or a consumer issue? THAT is moreso the question i think.

In almost every environment where the customer does his part and the tech does his part i havent seen any overheating issues.

Just my.02 worth