A business is only as good as its equipment and infrastructure. If the business has failing equipment, they will look less professional in the eyes of not only their customers but in the eyes of their stockholders also. There is no reason that a company as profitable as UPS cannot maintain their planes.
Yes, it is very important for companies like UPS to invest in the maintenance of their freight carrying aircraft and other vehicles. Consumers pay high costs of shipping for their packages and mail to be delivered, and they do not expect their deliveries to be harmed due to an accident involving a poorly maintained vehicle. This is unacceptable, and should any of the contents of the freighter have been harmed, UPS is surely responsible to pay reparations for the damages.
The biggest problem with these big corporations is that they are more concerned about saving money than putting that money towards safety. Human life is more important than the few dollars you save to cut corners. People work hard and they deserve to be treated with respect instead of being treated like a figure head.
Yes, companies should invest more in the maintenance of their freight carrying aircraft. If companies want to keep their reputations intact, they should do everything in their power to insure the safety of their equipment. If a company's equipment is found to be faulty, they will get less business and therefore less money. If a company decides not to invest more, however, that is the company's prerogative.