Surveillance - that's what supervisors are for. Really though, you have 800-1000 packages to load into 3-4 cars over 3-5 hours. When you have 20 of these bikes arrive on the conveyor belt in a 30 minute window and nowhere to put them (since it's hours from shift end and you can't put them in the delivery truck yet), they get dealt with fast and not so gently. That could easily mean a 3-4 ft drop onto concrete, and a supervisor would be unlikely to care since they know the pressure to go fast. The official policy is "hand to surface" for every package, but in reality you have to work at a pace where this is impractical - so it's ignored apart from egregious abuse of packages.
edit: as for discussion elsewhere here about proper packaging, here's FedEx guidelines/testing: http://www.fedex.com/us/services/pdf/PKG_Testing_Under150Lbs...
Some of the criteria, such as dropping the package 10x from a 30" height, might seem absurd if you haven't seen how the sausage is made. It really isn't.