this is actually a rational policy, not because they can't keep track of it, but because each entry in a expense report should be documented. if your reimbursements are ultimately charged to clients, then each expense needs to be separately documented. so even if the actual expenditure never changes, the ultimate payor might.

in my "expenses" folder on my laptop, i keep already-made pdf's of google maps that document the mileage to regular destinations, and just print a copy when appropriate. if i fly from the same airport for more than one client, each gets their own copy.